scispace - formally typeset
Search or ask a question

Showing papers in "Materials Science and Engineering A-structural Materials Properties Microstructure and Processing in 1999"


Journal ArticleDOI
TL;DR: In this article, the authors present 10 less-obvious, but very important, reasons for nitinol's success, both past and future, including the quickly growing and technologically demanding stent applications.
Abstract: Superelastic nitinol is now a common and well-known engineering material in the medical industry. While the greater flexibility of the alloy drives many of the applications, there are actually a large number of lesser-known advantages of nitinol in medical devices. This paper reviews 10 of these less-obvious, but very important, reasons for nitinol’s success, both past and future. Several new medical applications will be used to exemplify these points, including the quickly growing and technologically demanding stent applications. Stents are particularly interesting in that they involve new and complex manufacturing techniques, present a demanding and interesting fatigue environment, and most interestingly, take advantage of the thermoelastic hysteresis of nitinol.

1,446 citations


Journal ArticleDOI
TL;DR: In this article, the authors stress the need for further exploration of the 4P-relation: principles-properties-processing-products as well as in companies as well in universities or other research laboratories, illustrated by describing some actual applications indicating why they are successful, other applications why they failed and still others that can only be realised if some further, probably possible, material improvement can be realised.
Abstract: The diversity of (potential) applications using shape memory alloys (SMA), apart from the medical field, becomes quite large. Classic categories such as free recovery, actuators, constrained recovery, pseudo-elasticity or damping require further specifications. For example, micro-actuators, smart materials or active damping, can be all classified as actuator applications, but each of those items demands specific functional performance, dimensions and processing. Furthermore, success for applications can only be realised in so far those materials offer also a price-competitive advantage relative to other functional materials or mechanical designs. This competition requires perfect control of the material performance. It is known that especially Ni–Ti alloys can be tuned relatively easy to some specific requirements of the envisaged application: hysteresis, transformation temperatures, damping capacity. At the other side little is known on recovery stresses, wear resistance, fracture mechanics, fatigue … In this paper we would like to stress the need for further exploration of the 4P-relation: principles–properties–processing–products as well in companies as in universities or other research laboratories. This will be illustrated by describing some actual applications indicating why they are successful, other applications why they failed and still others that can only be realised if some further, probably possible, material improvement can be realised.

816 citations


Journal ArticleDOI
TL;DR: In this paper, the authors reviewed the strengthening mechanisms associated with the various components of martensitic microstructures in steels and other ferrous alloys and examined the experiments and strengthening theories associated with FeNi and FeNi-C alloys, in which the martensite, because of subzero temperatures, can be evaluated with carbon atoms trapped in octahedral interstitial sites.
Abstract: This paper reviews the strengthening mechanisms associated with the various components of martensitic microstructures in steels and other ferrous alloys. The first section examines the experiments and strengthening theories associated with Fe–Ni and Fe–Ni–C alloys, in which the martensite, because of subzero Ms temperatures, can be evaluated with carbon atoms trapped in octahedral interstitial sites. The evaluation of strengthening in these alloys has been limited to interpreting yield strength of unaged, untempered martensite in terms of interstitial solid solution strengthening. The second section reviews strengthening of martensitic Fe–C alloys and low-alloy carbon steels with above-room-temperature Ms temperatures. In these alloys, it is impossible to prevent C diffusion during quenching, and strengthening of martensite becomes dependent on static and dynamic strain aging due to carbon atom interaction with dislocation substructure. In all alloys the dominant strengthening component of martensitic microstructures is the matrix of martensitic crystals, either in lath or plate morphology, but secondary effects due to other microstructural components such as carbides and retained austenite are also discussed.

720 citations


Journal ArticleDOI
Vladimir Segal1
TL;DR: In this article, the authors present a continual analysis of stress, strain, shear planes, steady and localized flow, multipass processing which define microstructural effects and are critical for attained results.
Abstract: A special deformation technique, equal channel angular extrusion, (ECAE) to control materials structure, texture and physico-mechanical properties is described in detail. The paper presents a continual analysis of stress, strain, shear planes, steady and localized flow, multipass processing which define microstructural effects and are critical for attained results. Links between macromechanics of simple shear and grain refinement are outlined.

673 citations


Journal ArticleDOI
Zhijie Jia1, Zhengyuan Wang1, Cailu Xu1, Ji Liang1, Bingqing Wei1, Dehai Wu1, Shaowen Zhu1 
TL;DR: In this article, the experimental results show that carbon nanotubes (CNTs) can be initiated by AIBN to open their π-bonds, which imply that CNTs may participate in PMMA polymerization and form a strong combining interface between the CNT and the PMMA matrix.
Abstract: Carbon nanotubes (CNTs) can be used to compound poly (methyl methacrylate)/carbon nanotube (PMMA/CNT) composites by an in situ process. The experimental results show that CNTs can be initiated by AIBN to open their π-bonds, which imply that CNTs may participate in PMMA polymerization and form a strong combining interface between the CNTs and the PMMA matrix. Through the use of an improved in situ process, the mechanical properties and the heat deflection temperatures of composites rise with the increase of CNTs. The dispersion ratio of CNTs in the PMMA matrix is proportional to the reaction time of polymerizing MMA before CNTs are added into the PMMA mixture.

637 citations


Journal ArticleDOI
TL;DR: In this article, the authors examined gamma titanium-aluminide alloys, from the perspective of their balance of engineering properties, state of maturity, and prospects for impacting industrial needs.
Abstract: In the late 1970s and early 1980s, intermetallic phases emerged from being alloys of laboratory curiosity, or precipitate structures to be avoided or controlled in many ‘real metals’, to being widely investigated alloys, especially as prospective structural materials. After nearly two decades of sustained world-wide research, selected materials are emerging with a balance of properties which improves engineered systems, while others are introducing compelling research questions and prospects for significantly improved materials. This manuscript briefly examines selected intermetallic alloys and how they compete with other structural materials. The examination focuses on gamma titanium–aluminide alloys, from the perspective of their balance of engineering properties, state of maturity, and prospects for impacting industrial needs. A variety of engineering and business challenges remain to be solved, some of which are discussed.

484 citations


Journal ArticleDOI
TL;DR: In this article, the uniaxial compressive and tensile modulus and strength of several aluminum foams are compared with models for cellular solids, and the closed cell foams have moduli and strength that fall well below the expected values.
Abstract: The uniaxial compressive and tensile modulus and strength of several aluminum foams are compared with models for cellular solids. The open cell foam is well described by the model. The closed cell foams have moduli and strengths that fall well below the expected values. The reduced values are the result of defects in the cellular microstructure which cause bending rather than stretching of the cell walls. Measurement and modelling of the curvature and corrugations in the cell walls suggests that these two features account for most of the reduction in properties in closed cell foams.

479 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of process variables on flow response and microstructure evolution during hot working of Ti-6Al-4V with a colony alpha preform micro-structure was established using isothermal hot compression tests.
Abstract: The effect of process variables on flow response and microstructure evolution during hot working of Ti–6Al–4V with a colony alpha preform microstructure was established using isothermal hot compression tests. Testing was conducted on material with prior-beta grain sizes of 100 μm or 400 μm at strain rates of 0.001–10 s−1, test temperatures between 815 and 955°C, and height reductions of 40–80%. All of the flow curves exhibited a peak stress followed by moderate flow softening. The absence of a grain/colony size dependence of flow behavior, coupled with relatively low values of the strain rate sensitivity of the flow stress (∼0.05–0.30), led to the conclusion that deformation was controlled by dislocation glide/climb processes. Flow softening was interpreted in terms of deformation heating and substructure/texture evolution. The dependence on strain rate and temperature of the kinetics of dynamic globularization of the colony microstructure was complex and appeared to be of second-order importance compared to the effects of strain per se, thus suggesting the dominance of dislocation-type processes for the control of globularization as well.

399 citations


Journal ArticleDOI
TL;DR: In this paper, an epitaxial laser metal forming (E-LMF) is presented as a new cladding technique which combines the advantage of near-net-shape manufacturing with a close control of the solidification microstructure.
Abstract: Epitaxial laser metal forming (E-LMF) is presented as a new cladding technique which combines the advantage of near-net-shape manufacturing with a close control of the solidification microstructure. E-LMF is a process where metal powder is injected into a molten pool formed by controlled laser heating. Laser surface treatment has the advantage that heat input is very localised, thus leading to large temperature gradients. This is used, in unison with closely controlled solidification velocities, to stabilise the columnar dendritic growth, thereby avoiding nucleation and growth of equiaxed grains in the laser clad. It is possible with this technique to deposit a single crystal clad by epitaxial growth onto a single crystal substrate. In this paper, the microstructure obtained by E-LMF is analysed by scanning electron microscopy (SEM), optical microscopy (OM) and indexing electron backscattered diffraction (EBSD) patterns. In particular, the grain structure formation in the deposit during the process and the influence of a subsequent heat treatment on precipitation and recrystallisation is characterised.

372 citations


Journal ArticleDOI
TL;DR: In this paper, the influence of mechanical surface treatments on magnesium fatigue strength was investigated in relation to the relatively well-studied titanium and aluminum alloys, and the results showed that these changes can have contradictory influences on the fatigue strength.
Abstract: Generally, mechanical surface treatments induce high dislocation densities in near-surface regions. Due to the local plastic deformation, residual stresses are developed and the surface topography is changed. These changes can have contradictory influences on the fatigue strength. Results on the influence of mechanical surface treatments on magnesium are presented in relation to the relatively well-studied titanium and aluminum alloys.

370 citations


Journal ArticleDOI
TL;DR: In this article, the authors reviewed the recent development of the above mentioned topics relating to sputter-deposited TiNi-base shape memory alloy thin films and found unique microstructures consisting of nonequilibrium nanoscale precipitates.
Abstract: Since 1990, TiNi and TiNiX (X=Cu, Pd, Hf) thin films have been made by sputtering The motivation for fabricating sputter-deposited TiNi-base shape memory alloy thin films originates from the great demand for the development of powerful microactuators which can drive micromachines, because actuation force and displacement are greatest in shape memory alloys amongst many actuator materials Stable shape memory effect and superelasticity, which are equivalent to those of bulk alloys, have been achieved in the sputter-deposited TiNi thin films Narrow transformation temperature hysteresis and high transformation temperatures were also achieved in TiNiCu and TiNi(Pd or Hf) thin films, respectively In the meantime, unique microstructures consisting of nonequilibrium nanoscale precipitates and nonequilibrium compositions in the matrix have been found in Ti-rich TiNi thin films which were fabricated from amorphous condition by annealing at a considerably low temperature Several micromachining processes have been proposed to fabricate some prototypes of microactuators utilizing TiNi thin films The present paper will review the recent development of the above mentioned topics relating to sputter-deposited TiNi-base shape memory alloy thin films

Journal ArticleDOI
TL;DR: In this article, the evolution during heat treatment of the as-forged microstructure of the high strength superalloy UDIMET 720Li has been studied and the results have implications for the gas turbine manufacturers.
Abstract: The evolution during heat treatment of the as-forged microstructure of the high strength superalloy UDIMET 720Li has been studied. Particular emphasis has been placed on the characterisation of γ ′ precipitation kinetics using optical and transmission electron microscopies (TEM) and subsequent image analysis. The observations are interpreted using thermodynamic, phase transformation and precipitate hardening theories. The results have implications for the gas turbine manufacturers. Through a better understanding of the evolution of the microstructure during ageing, a heat treatment of 24 h at 700°C is proposed, which is believed to be optimal. This allows full advantage to be taken of the properties of the alloy, whilst reducing the costs and time associated with the heat treatment schedules. Moreover, the data presented allows the variation in properties across a U720Li forging to be estimated.

Journal ArticleDOI
TL;DR: In this paper, the authors visualized the dynamics of superplastic flow in friction-stir welding of 0.6 cm plates of 2024 Al (140 HV) to 6061 Al (100 HV).
Abstract: The friction-stir welding (FSW) of 0.6 cm plates of 2024 Al (140 HV) to 6061 Al (100 HV) is characterized by residual, equiaxed grains within the weld zone having average sizes ranging from 1 to 15 μm, exhibiting grain growth from dynamically recrystallized grains which provide a mechanism for superplastic flow; producing intercalated, lamellar-like flow patterns. These flow patterns are visualized by differential etching of the 2024 Al producing contrast relative to 6061 Al. The flow patterns are observed to be complex spirals and vortex-like, among others, and to change somewhat systematically with tool rotation (stirring) speed between 400 and 1200 rpm; depending on tool orientation. The equiaxed grain and sub-grain microstructures are observed to vary according to estimated temperature profiles (varying from 0.6 to 0.8 TM, where TM is the absolute melting temperature) referenced to the rotating tool axis. Dislocation spirals and loops are also observed in the 2024 Al intercalation regions within the weld zones at higher speeds (>800 rpm) corresponding to slightly elevated temperatures introducing dislocation climb, and residual microhardness profiles follow microstructural variations which result in a 40% reduction in the 6061 Al workpiece microhardness and a 50% reduction in the 2024 Al workpiece microhardness just outside the FSW zone.

Journal ArticleDOI
TL;DR: In this article, the shape memory mechanisms of Fe-based alloys are discussed based on microscopic observations with various scales ranging from micron meter to sub-nanometer, and the following conditions are the most important ones to achieve a good shape memory effect: a low twin-boundary energy in martensite is an important factor to reduce the density of dislocations residing at the austenite-martensite interface and make easy the reverse movement of the interface.
Abstract: Shape memory mechanisms, characteristic of Fe-based alloys, are discussed based on the microscopic observations with various scales ranging from micron meter to sub-nanometer. Most of the Fe-based shape memory alloys that may be technologically applicable in the future are associated with the fcc/bct and fcc/hcp transformations. The modes of the stress-induced martensitic transformation and its reverse transformation in these transformation systems, which are directly related to the shape memory effect, are examined in detail and it is concluded that the following conditions are the most important ones to achieve a good shape memory effect. In the case of the fcc/bct transformation, the tetragonality of the bct martensite must be large so that the twin boundary energy in martensite can be lowered, which results in that very fine transformation twins are completely extended through a martensite plate. A low twin-boundary energy in martensite is an important factor to reduce the density of dislocations residing at the austenite–martensite interface and make easy the reverse movement of the interface. In the extreme case of no dislocations at the interface, a thermoelastic transformation will be realized. A higher yield stress for slip in bct martensite is another factor to bring about the reversibly mobile interface. These are deduced from the detailed analysis of dislocations generated behind the reverse-moving interface on heating. In the case of the fcc/hcp transformation, the formation of extremely thin hcp martensite plates with uniform distribution in a deformed sample is most required to achieve a good shape memory effect. For such thin martensite plates to be produced, high densities of stacking faults must preexist on the primary slip system in austenite when an external stress is applied for shape change. A new mechanism for the formation of very thin martensite plates by an applied stress is presented. A low stress for inducing martensite transformation compared with the yield stress for slip in austenite, which results from the so-called ‘training’ treatment, may be a necessary but not sufficient condition for obtaining a good shape memory effect. Future directions of the research on Fe-based shape memory alloys are suggested.

Journal ArticleDOI
TL;DR: In this article, applied and residual lattice strains were determined by neutron diffraction during a tensile test of a weakly textured austenitic stainless steel and were compared to the predictions of a self-consistent polycrystal deformation model.
Abstract: Applied and residual lattice strains were determined by neutron diffraction during a tensile test of a weakly textured austenitic stainless steel and were compared to the predictions of a self-consistent polycrystal deformation model. Parallel to the tensile axis the model predictions are generally within the resolution of the diffraction measurements, but perpendicular to the tensile axis discrepancies are noted. Discrepancies between model and measurements were greater for the residual lattice strains than during loading. It is postulated that this is because the model does not predict reverse plasticity during unload.

Journal ArticleDOI
TL;DR: In this paper, an overview of high temperature structural silicide research and development is presented in the areas of materials, composites, and applications, focusing on glass processing, wear resistance, diesel engine glow plugs, and aerospace components.
Abstract: Significant progress has been made in the past few years in both the scientific understanding of high temperature structural silicides and in their technological development. This overview highlights key aspects of this structural silicide research and development, in the areas of materials, composites, and applications. Silicide materials discussed are MoSi2, Mo5Si3, Mo<5Si3C<1, Ti5Si3, and C40 type silicides. Results on MoSi2–Si3N4, MoSi2–SiC, MoSi2–Al2O3, and MoSi2–Si3N4–SiC composites are summarized. Finally, selected applications in glass processing, wear resistance, diesel engine glow plugs, and aerospace components are described.

Journal ArticleDOI
TL;DR: In this paper, the AISI 304 was shot peened or deep rolled with different peening intensities, and rolling pressures, respectively, and the resulting near surface properties were characterized by cross sectioning transmission electron microscopy (TEM), residual stress and phase analysis as well as interference line halfwidth and microhardness measurements.
Abstract: Cylindrical specimens of the austenitic stainless steel AISI 304 were shot peened or deep rolled with different peening intensities, and rolling pressures, respectively. The resulting near surface properties were characterized by cross sectioning transmission electron microscopy (TEM), residual stress and phase analysis as well as interference line half-width and microhardness measurements. Cyclic deformation curves were obtained by hysteresis measurements under stress control with zero mean stress. The microstructural alterations in the fatigued surface regions were again characterized by the above mentioned methods. The investigations revealed that both shot peening and deep rolling lead to a complex near surface microstructure, consisting of nanocrystalline regions, deformation bands and strain induced martensitic twin lamellae with high dislocation densities in the austenitic matrix. These microstructural changes severely influence the cyclic deformation behaviour: Plastic strain amplitudes and cyclic creep were drastically decreased by shot peening and especially by deep rolling. Both surface finishing methods were found to decrease crack initiation and propagation rate. Remarkably, the initial residual stress profile and surface strain hardening were not completely eliminated even by applying high cyclic stress amplitudes. This is due to the fact that during cyclic loading dislocation cell structures were only formed in greater depths whereas the nanocrystalline layer remained stable. In the case of deep rolled surfaces, the martensitic layer was even increased by fatigue-induced martensite formation.

Journal ArticleDOI
TL;DR: In this paper, a theoretical methodology for the design and development of low modulus Ti alloys and/or structures is provided by means of electronic structural calculations using the discrete variational cluster method (DVM).
Abstract: Titanium alloys are favorable implant materials for orthopedic applications, due to their desirable mechanical properties and biochemical compatibility (or bio-inertness). However, current bio-titanium alloys still possess too high an elastic modulus compared with that of the bone, which can lead to premature failure of the implant. Here, a theoretical methodology for the design and development of low modulus Ti alloys and/or structures is provided by means of electronic structural calculations using the discrete variational cluster method (DVM). The preliminary study concentrated on two β-Ti atomic clusters consisting of 15, and 27 atoms, respectively. The binding energies between titanium and various alloying atoms within the clusters were first calculated, from which strength and modulus were then estimated. The results of the calculation suggested that Nb, Mo, Zr and Ta were suitable alloying elements for β-type titanium alloys, capable of enhancing the strength and reducing the modulus of the materials.

Journal ArticleDOI
TL;DR: In this article, an investigation of precipitation in an industrial Al-Zn-Mg alloy at various stages of a conventional two-step ageing treatment at 100° and 150°C was performed using both transmission electron microscopy and atom-probe field ion microscopy.
Abstract: Fine-scale precipitation of the metastable Zn- and Mg-rich η′ phase and its precursors is essential for the mechanical properties of Al–Zn–Mg alloys. However, at present neither the precipitation sequence nor the structure and composition of the intermediate precipitate phases are completely clear. This paper deals with an investigation of precipitation in an industrial Al–Zn–Mg alloy at various stages of a conventional two-step ageing treatment at 100° and 150°C. Studies were performed using both transmission electron microscopy and atom-probe field ion microscopy. Transmission electron microscopy (TEM) analysis revealed two parallel precipitation paths; one involving formation and dissolution of the ordered GP (I) zones, the other involving formation of clusters (type II), having a different atomic arrangement compared to the Al-matrix, which transform to the η′ phase. Atom-probe study of the material after short time ageing at 100°C did not show any observable distinction between GP (I) and type II precipitates. In the peak-aged material the best classification of precipitates was obtained using their morphology (the cigar-like and the plate-like) because there was significant overlap in the range of total solute contents of each type of precipitate. Generally the Zn:Mg ratio in all observed types of precipitates was close to 1:1 and the total solute atom content increased with ageing time. Distribution of alloying elements in the precipitates and in the surrounding matrix is discussed.

Journal ArticleDOI
TL;DR: In this article, the effect of deformation mode and plastic strain over a large strain range on the microstructural evolution and mechanical behaviour of aluminium was discussed and the average misorientation across the deformation induced boundaries is ∼25°.
Abstract: Polycrystalline pure aluminium (99.99%) has been deformed at room temperature by the Cyclic-Extrusion–Compression (CEC)-method to strains in the range 0.9–60 (1–67 cycles). At different strains, the microstructure and local crystallography have been characterised in particular by transmission electron microscopy. It has been found that the microstructure develops from a cell block structure into an almost equiaxed structure of cells and subgrains, that the spacing between the boundaries subdividing the structure is almost unaffected by the strain and that the misorientation across these boundaries increases with the strain over the whole strain range. At the largest strain, the average misorientation across the deformation induced boundaries is ∼25°. The flow stress in compression is measured after the cyclic deformation and it is found that the flow stress increases with strain towards a saturation level which is reached at a relatively low strain. The discussion comprises the effect of deformation mode and plastic strain over a large strain range on the microstructural evolution and mechanical behaviour of aluminium.

Journal ArticleDOI
TL;DR: In this paper, the chemical properties of metallic biomaterials used for artificial joints, bone plates, and dental implants in vivo are discussed based on empirical data, focusing on the maturation of surface oxide film on titanium and the film's destruction and regeneration in body fluids.
Abstract: The chemical properties of metallic biomaterials used for artificial joints, bone plates, and dental implants in vivo are discussed based on empirical data, focusing on the maturation of surface oxide film on titanium and the film’s destruction and regeneration in body fluids. It is reviewed the behavior of metallic materials in vivo and how to modify the surface of biomaterials to improve corrosion and wear resistance and bone conductivity. Effect of calcium ion implantation into titanium for improvement of its bone conductivity is given as an example.

Journal ArticleDOI
TL;DR: In this paper, the development and application of titanium alloys for manufacturing engineering structures for the extraction of hydrocarbons in the offshore zone of Russia is discussed. And the authors conclude on the expediency and efficiency of the use of the alloys is based on the analysis of operating conditions and experience in the operation of titanium alloy in vessel structures and power plants.
Abstract: The paper covers some problems of the development and application of titanium alloys for manufacturing engineering structures for the extraction of hydrocarbons in the offshore zone of Russia. The conclusion on the expediency and efficiency of the use of titanium alloys is based on the analysis of operating conditions and experience in the operation of titanium alloys in vessel structures and power plants.

Journal ArticleDOI
TL;DR: An overview of boundary diffusion theory with emphasis on the interpretation of concentration profiles measured in diffusion experiments is given in this article, where the authors consider the most important situations encountered in boundary diffusion experiments, such as diffusion in the B and C regimes.
Abstract: Grain boundary (GB) diffusion often controls the evolution of structure and properties of engineering materials at elevated temperatures. A knowledge of diffusion characteristics of GBs and deep fundamental understanding of this phenomenon are critical to many materials applications. In this paper we give an overview of boundary diffusion theory with emphasis on the interpretation of concentration profiles measured in diffusion experiments. We consider the most important situations encountered in boundary diffusion experiments, such as diffusion in the B and C regimes and diffusion in the presence of segregation. We also discuss the recent progress in the atomistic interpretation of GB diffusion. We conclude with an outlook for future research in this area.

Journal ArticleDOI
TL;DR: In this paper, Molybdenum boron silicides consisting of 20-50 vol.% of α-Mo and different ratios of the intermetallic phases Mo5SiB2 (T2) and Mo3Si were prepared by arc-melting followed by dropcasting into Cu chill molds.
Abstract: Molybdenum boron silicides consisting of 20–50 vol.% of α-Mo and different ratios of the intermetallic phases Mo5SiB2 (‘T2’) and Mo3Si were prepared by arc-melting followed by dropcasting into Cu chill molds. For α-Mo volume fractions of ≈50% sound castings were obtained. For lower α-Mo volume fractions such as 25% macroscopic cracks were often observed. Preliminary oxidation tests verified the expected increase in the oxidation resistance as the B-concentration increases and the α-Mo volume fraction decreases. Also, the formation of glass films was observed. Depending on composition and heat treatment, the room temperature flexure strengths varied usually between 300 and 600 MPa. To some extent, these variations could be rationalized by differences in the microstructures. Annealing for 1 day at 1873 K in vacuum caused distinct microstructural coarsening. Annealing was sometimes accompanied by microcracking in the Mo3Si and the T2 phases. Cooling curves suggest that the liquidus temperature of the T2 phase is above 2400 K. Depending on the composition, final freezing of Mo–Si–B alloys was found to occur at temperatures as low as 2200 K. Care is therefore required during thermomechanical processing to avoid the formation of liquid phases.

Journal ArticleDOI
TL;DR: In this article, a SiC/SiC ceramic matrix composite material for aeronautic combustor liner applications is presented. But, the effects of the aggressive combustion environment continue to be a material system development challenge.
Abstract: Significant progress has been made developing a SiC/SiC ceramic matrix composite material for aeronautic combustor liner applications. Improvements in material processing technology have resulted in improved thermal conductivity and fatigue durability. A material characterization effort is underway to assess material behavior and direct material development efforts. The effects of the aggressive combustion environment continue to be a material system development challenge.

Journal ArticleDOI
TL;DR: In this paper, a rotary bending fatigue tester was used to measure the fatigue life of TiNi and TiNi-10Cu alloys, which were annealed at 673 K for 3.6 ks.
Abstract: Fatigue lives of Ti–Ni and Ti–Ni–10Cu alloys were measured using a rotary bending fatigue tester. The fatigue tests were carried out at 308, 323, 338, 368, and 398 K, respectively, under a constant strain amplitude condition. The Af points of Ti–Ni and Ti–Ni–10Cu alloys, which were annealed at 673 K for 3.6 ks, were 351 and 331 K, respectively. Two types of strain amplitude vs fatigue life curves were observed, one composed of two straight lines with one turning point whereas the other composed of three straight lines with two turning points. The upper turning point coincided with the elastic limit strain and the lower one with the proportional limit strain. The single turning point was observed in a fatigue test condition under which both the limit strains are almost the same. The fatigue life decreased with increasing test temperature in general. However, it became less sensitive to test temperature both in higher and lower temperature regions. Deformation mode and applied stress during fatigue testing are factors affecting fatigue life. However, the fatigue life of the Ti–50.0 at.% Ni is always longer than that of the Ti–40Ni–10Cu (at.%) if the fatigue life is plotted as a function of temperature difference between test temperature and Ms.

Journal ArticleDOI
TL;DR: In this paper, the effect of crystallographic orientation on fracture toughness and the fracture path of silicon single crystal was investigated Vickers microhardness indentation was used to introduce cracks along various crystallographic orientations on the (110, (001), and (111) planes.
Abstract: In this study the effect of crystallographic orientation on fracture toughness and the fracture path of silicon single crystal was investigated Vickers microhardness indentation was used to introduce cracks along various crystallographic orientations on the (110), (001), and (111) planes The fracture toughness variation was found to follow the symmetry of the indentation axis with no distinct correlation with the elastic constants The observations made suggest that the inclination angle of cleavage planes relative to the indent plane affects the fracture path and toughness significantly Prestraining decreased the hardness and improved the toughness without a modification of fracture path

Journal ArticleDOI
TL;DR: In this article, the substrate temperature effects have been studied in an integrated manner relating the initial splat formation to microstructure development and eventually to the properties of the deposit, and the results confirm that there exists a threshold transition temperature for the substrate surface beyond which the splat morphology changes from a fragmented (splashed) to a more contiguous (disk-shaped) morphology.
Abstract: In recent years it has been observed that the substrate surface temperature during thermal spray deposition has a profound effect on the morphology of the impacted droplet (splat) and consequently on the microstructure and properties of the deposits. In this set of two papers (one for metal and one for ceramic), the substrate temperature effects have been studied in an integrated manner relating the initial splat formation to microstructure development and eventually to the properties of the deposit. Isolated impacted splats have been obtained on polished steel substrates at two different temperatures (high and low) and these have been analyzed quantitatively for their shape factors and thicknesses. The deposits have been formed nominally at these two different temperatures and their microstructures and properties have been analyzed. The results confirm that there exists a threshold transition temperature for the substrate surface beyond which the splat morphology changes from a fragmented (splashed) to a more contiguous (disk-shaped) morphology. In the case of zirconia this temperature appears to be in the range of about 250‐300°C, which is roughly 10% of the melting temperature of zirconia. It has been further observed that the splat‐substrate and inter-splat contact is significantly improved at higher temperatures, leading to reduced porosity, increased thermal conductivity and strength. These results are assimilated to develop an integrated structure‐property relationship and preliminary arguments are presented as to the reason for such transitions. © 1999 Elsevier Science S.A. All rights reserved.

Journal ArticleDOI
TL;DR: A great deal of research, over many decades, has revealed substantial information about the mechanism of the bainite transformation in steels as mentioned in this paper, which are now routinely being used in many parts of the world in the design of novel alloys and in the interpretation of a variety of experimental data.
Abstract: A great deal of research, over many decades since the discovery of bainite, has revealed substantial information about the mechanism of the bainite transformation in steels. Elements of the theory are now routinely being used in many parts of the world in the design of novel alloys and in the interpretation of a variety of experimental data. However, there remain some difficulties which are holding up technological progress. Two of these, the precipitation of carbides and the formation of bainite from plastically deformed austenite, are reviewed in the hope that further progress can be stimulated, particularly with respect to the development of quantitative models.

Journal ArticleDOI
TL;DR: In this paper, equal channel angular (ECA) pressing was used to introduce ultrafine grain sizes in pure Al, Al-Mg and Al-Zr alloys, with grain sizes lying in the sub-micrometer range for alloys.
Abstract: Superplastic deformation occurs at high temperatures and requires the presence of a very small grain size. Experiments demonstrate that equal-channel angular (ECA) pressing is capable of introducing ultrafine grain sizes in pure Al, Al–Mg and Al–Zr alloys, with grain sizes lying in the sub-micrometer range for the alloys. It is shown by static annealing that these ultrafine grain sizes are not stable in pure Al and the Al–Mg alloys at elevated temperatures but in the Al–Zr alloys the grains remain small up to temperatures of ≈600 K.