Showing papers on "Alloy published in 1980"

Cohesion in alloys - fundamentals of a semi-empirical model

Abstract: A semi-empirical model of alloy cohesion involving two material constants for each element is introduced by means of the physical ideas underlying the scheme The resulting expressions for the heat of formation of binary alloys are presented and their applicability in various extreme situations is discussed The model is shown to reproduce a vast amount of experimental information on the sign of heats of formation Detailed comparison with experiment for particular classes of alloys will be presented in the sequels to this paper

Self-diffusion in austenitic Fe-Cr-Ni alloys

Abstract: The simultaneous lattice diffusion of 59Fe, 51Cr and 57Ni tracers has been measured in the alloys Fe-15Cr-20Ni, Fe-15Cr-45Ni, Fe-22Cr-45Ni and Fe-15Cr-20Ni-1.4Si between 960 and 1400 degrees C. In all four alloys at all temperatures, DCr>DFe>DNi, with DCr/DNi approximately=2.5 and DFe/DNi approximately=1.8. The activation enthalpies for diffusion of the major constituents in any one alloy are quite close to each other. No correlation is found between swelling under irradiation and the diffusion behaviour of the major constituents. The results are discussed on the basis of the random-alloy model. Grain-boundary diffusion is found in these alloys at surprisingly high temperatures.

Phase transformations and tensile properties of Ti-10V-2Fe-3AI

Abstract: The effect of heat treatment on the microstructure of the metastableα-Ti alloy Ti-10V-2Fe-3Al has been studied using light and electron metallography, analytical electron microscopy, and X-ray diffraction. A survey of the effects of microstructure on tensile properties of the alloy also has been conducted. It has been found that the alloy contains inclusions which are rich in Ti, S, Si, and P. The alloy has been shown to form ω-phase both athermally and isothermally. The isothermal ω can have either an ellipsoidal or a cuboidal morphology. The reasons for this are enumerated. The formation of α-phase has been studied, and three distinct modes of formation are described. A stress induced orthorhombic martensite also has been observed. The effect of this stress induced product on tensile behavior is discussed. The relative roles of inclusions and α-phase precipitates in the tensile fracture also have been examined.

A micromorphological study of the dissolution of silver-gold alloys in nitric acid

Abstract: Microscopic observations of the surface structure and composition of thin films of silver-gold alloys are used to deduce the processes involved in the dissolution of these alloys in nitric acid solutions. The micromorphology consists of an island-and-channel structure whose formation depends in detail on the initial overall composition of the alloy. The micromorphology can be modified by annealing for short times at elevated temperature, by storage for long periods at room temperature, or by increasing the strength of the acid during corrosion, giving very similar results. These observations can be explained in terms of a model in which corrosion proceeds by selective dissolution of the less noble component, thereby creating a disordered surface layer which subsequently reorders by surface diffusion.

Carbide reactions (M3C→M7C3→M23C6→M6C) during tempering of rapidly solidified high carbon Cr-W and Cr-Mo steels

Abstract: Carbide transformations of M3C → M7C3 → M23C6 → M6C and crystallographic relationships among these carbides were examined by transmission electron microscopy. Two kinds of high carbon-chromium steels containing tungsten or molybdenum were quenched rapidly from the melts and tempered at temperatures up to 700°C. By tempering at 600°C, M7C3 carbides nucleated mostly on cementite/ferrite interfaces and grew inward the cementite byin- situ transformation.In-situ transformations from M7C3 to M23C6 and from M23C6 to M6C were also found in these alloy steels during tempering at higher temperatures. Mutual relationships of crystal orientations among M3C, M7C3, M23C6 and M6C were decided as follows: {fx739-01}.

The wetting of alumina by copper alloyed with titanium and other elements

Abstract: The wettability of alumina by ternary alloys of copper, titanium and aluminium, gallium gold, indium, nickel or silver has been investigated using sessile drop tests conducted in vacuum at 1050–1250° C. Substantial additions of titanium are known to induce copper to wet alumina due to the formation of a titanium rich reaction product at the alloy/ ceramic interface, but the present work has shown that the concentration of titanium can be reduced by the addition of ternary alloying elements. Additions of indium are very beneficial, of aluminium, gold or silver are moderately beneficial, and of gallium or nickel are of negligible benefit or detrimental. These observations, and previous work with copper-tin-titanium alloys [1] can be interpreted in terms of effects on the activity of titanium which it is argued will be enhanced if the ternary alloying element has a low surface energy and is readily saturated by titanium. The correlation of the experimental wetting observations with the surface energy and titanium solubility data for the ternary alloying elements provides a basis for the rational development of reactive metal brazes for joining unmetallized ceramics.

Methods of manufacturing gradient composite metallic structures

Abstract: A method is disclosed for forming roller cutters and also for forming cutting teeth for rolling cutter bits, including cutter inserts, cutter teeth formed in place, or formed separately and welded in place, etc., by powder metallurgy as a densified powder metallurgical composite of at least two varying phases, the composite having a substantially continuous mechanical property gradient therethrough. The gradient is from one region having hardness or wear resistant properties to another region having toughness properties. The method comprises:providing a first powder mixture comprising a major proportion by volume of a powdered refractory compound and a minor proportion by volume of a powdered binder metal or alloy. Providing a second powder comprising a powdered binder metal or alloy or a mixture comprising a powdered refractory material and a powdered binder metal or alloy, present in a lesser proportion by volume than in the first powder. Forming the cutter, or cutter teeth or inserts of the first and the second powders. Mixing the powders during or prior to the forming step and introducing into a first region of the mold a mixture having a larger proportion of the first powder relative to the second powder. Changing the relative proportions of the powders and introducing the mixture into a second region of the mold a mixture having a different proportion of the first powder relative to the second powder and a continuous gradient in the relative proportions of the powders between the regions. Densifying the powders into a solid member having a gradient in composition and properties from the first region to the second region.

Refractory silicides of titanium and tantalum for low-resistivity gates and interconnects

Abstract: A study of the refractory-gate metallization schemes had been undertaken to provide a low-resistivity metallization for LSI and VLSI. In this paper, we describe an overview of the efforts made in this direction and present two different metallization schemes which lead to a resistivity of ≤20 and 40 µΩ.cm at the gate level. These schemes involve formation of titanium and tantalum silicides on polysilicon gates, respectively. The recommended structure is a metal or a cosputtered alloy/polysilicon/gate oxide/substrate which, when sintered, gives the desired structure silicide/polysilicon/gate oxide substrate. By the use of 1000-A Ti or Ta, the sheet resistance of nearly 1 or 2 Ω/□, respectively, can be routinely obtained. The silicides are mechanically strong and can be dry etched using radial-flow or barrel-type plasma reactors. The Ta silicide structure is found to be very stable throughout standard processing and can be retrofitted in the present processing sequence. Ti silicide structures are similarly stable except for the reactivity of the silicide with HF-containing reagents. The Ti silicide metallization scheme can therefore be employed in processing with changes incorporated to avoid HF-silicide contact.

Structure-property relations and the design of Fe-4Cr-C base structural steels for high strength and toughness

Abstract: Some design guidelines for improving strength-toughness combinations in medium car-bon structural steels are critically reviewed. From this, quaternary alloy development based on Fe/Cr/C steels with Mn or Ni additions for improved properties is described. Transmission electron microscopy and X-ray analysis reveal increasing amounts of retained austenite in these alloys with Mn content up to 2 wt pct and Ni additions at 5 wt pct after quenching from 1100°C. A corresponding improvement in toughness properties is also found. Grain refining results in a further increase in the amount of retained austenite. In addition, the excellent combinations of strength and toughness in these quaternary alloys are attributed to the production of dislocated lath martensite from a homogeneous austenite phase free from undissolved alloy carbides. The question of thermal instability of retained austenite following tempering is considered in detail and it is shown that the decomposition of retained austenite is closely related to the ease of nucleation and growth of cementite. Thus, graphitizing alloying elements such as Ni are beneficial in postponing the decomposition of retained austenite.

Growth and Microstructure of α ‐ Al2 O 3 on Ni‐Al Alloys: Internal Precipitation and Transition to External Scale

Abstract: Oxidation properties of Ni‐2 and 6 w/o Al alloys were investigated in 1 atm oxygen at temperatures in the range 1273°–1573°K. Ni‐2 w/o Al oxidized parabolically, one order of magnitude more rapid than pure nickel, to a duplex scale by metal diffusion consisting of outer and inner layers of Al‐doped and , respectively, and an internal zone of rodlike precipitates by oxygen diffusion through the Al‐depleted alloy. Oxidation kinetics of Ni‐6 w/o Al alloy were irreproducible due to early‐stage formation of an imperfect scale containing nodules. Impingement of favorably oriented rodlike precipitates growing beneath the nodules accompanied with lateral diffusion of aluminum to react with oxygen at the precipitation front eventually led to transition from internal oxidation to development of a multilayered scale.

Embrittlement of ferritic stainless steels

Abstract: The mechanical properties and microstructures of commercial 11 to 29 pct Cr ferritic steels were examined as functions of aging times to 1000 h at 371, 482, and 593°C. Of the properties evaluated, changes in impact transition temperatures were the best measure of embrittlement. Embrittlement at 482°C occurs most rapidly in the 29 pct Cr alloy and somewhat more slowly in the stabilized 26 pct Cr alloy. The stabilized 18 pct Cr alloy embrittles much more slowly while little, if any, embrittlement was detected in a stabilizedll pct Cr alloy. Embrittlement at 482°C was characterized by a rapid change in properties followed by a plateau region and then further property changes. The early property change is attributed to precipitation of interstitial compounds and the later change to classic 475°C embrittlement. The onset of 475°C embrittlement in the two highest Cr alloys was accompanied by clustering of Cr atoms along {100} planes indicative of spinodal decomposition. Concurrent with clustering there was also a change from turbulent slip to a more planar slip along {110} planes. Some embrittlement was observed after longer exposures at 371°C which was attributed to a combination of 475°C embrittlement and the precipitation of interstitial compounds. Two of the alloys also embrittled at 593°C, accompanied by optically observable precipitates. The precipitate in the stabilized 18 pct Cr alloy was identified as Laves (Fe2Ti) phase. One of the precipitates in the 29 pct Cr alloy was identified as sigma phase.

The early stages of development of α-Al2O3 scales on Fe-Cr-Al and Fe-Cr-Al-Y Alloys at high temperature

Abstract: The development ofthe oxides on Fe-14%Cr-4%Al, Fe-27%Cr-4%Al, and similar alloys containing 0.008% Y, 0.023% Y, and 0.8% Y has been investigated during the early stages of oxidation in 1 atm oxygen at 1000 and 1200°C. In all cases, a steady-state α-Al2O3layer is established rapidly, after some initial formation of transient oxides rich in iron and chromium. For the yttrium-free alloys the steady-state situation is achieved more rapidly for the higher chromium-containing alloy and at the higher temperature. The amount of transient oxide formed is also determined by the specimen surface topography since the development of the α-Al2O3 layer is less rapid at the base of alloy asperities than at a flat alloy-oxide interface. Following establishment of the complete α-Al2O3layer, the oxide develops a convoluted oxide morphology at temperature, due to high compressive growth stresses in the oxide. These arise following reaction between oxygen ions diffusing inward down the oxide grain boundaries and aluminum ions diffusing outward through the bulk oxide. This results in lateral growth of the oxide and plastic deformation and movement of the alloy in a direction parallel to the alloy-oxide interface. The addition of yttrium to the alloys promotes the selective oxidation of aluminum. Also, the yttrium is incorporated into the growing oxide where it changes the mechanism of growth, reducing the production of the high compressive growth stresses and thus the development of the convoluted oxide morphology.

Energy absorption by foam filled structures

Abstract: The energy absorbed during the axial collapse of a variety of structures made in steel, aluminum alloy, and glass fiber reinforced plastic (GFRP) was examined with respect to changes produced by foam filling reinforcement. A simple model was devised which permits reasonable estimates of the axial collapse load for a structure and an assessment of the weight-effectiveness of foam filling for that structure. Design charts are given, from which the dimensions can be derived for sections made in either steel or aluminum alloys of any particular strength level, in order to establish foam weight-effectiveness. Foam filling is primarily of value only in sections made from high density, low strength materials, e.g. mild steel. It becomes weight-effective in sections having a thickness-to-section size ratio of less than about .02. In the case of brittle materials (e.g. GFRP), foam filling promotes the crush stability of the structure. Such stability improvements may be the major need for foam filling in these sections and also in large, thin-wall metal sections.

Aluminum-transition metal alloys made using rapidly solidified powers and method

Abstract: A method of fabricating aluminum alloys containing finely dispersed aluminum-transition metal intermetallic phases is disclosed. The alloys are subjected to melt spinning to form a brittle filament consisting in large measure of a metastable face-centered cubic solid solution; this is then pulverized to a staple or powder configuration; the power or staple is consolidated using conventional techniques. Upon heat treatment, the solid solution decomposes into a structure consisting of an aluminum alloy matrix of conventional composition containing a fine uniform dispersion of the intermetallic phase, the heat-treated alloy being ductile. The heat-treated alloys possess high strength, especially at elevated temperatures. Preferred alloys are disclosed which contain 10 to 15 wt % Fe.

The development of localized pits during stainless steel oxidation

Abstract: A study of the localized pitting attack of 20% Cr/25%Ni stainless steel and a similar alloy containing a dispersion of titanium nitride particles has been made over the temperature range 1023 to 1173 K. Pitting is initiated when localized spoiling of the protective chromic oxide film occurs. Rapid oxidation of the chromium-depleted substrate then proceeds with the formation of an iron-rich oxide mound on the alloy surface and spinels containing nickel, chromium, and iron within the pit itself. A silica layer which, in general, remains on the alloy surface acts as a diffusion barrier during this stage of the reaction. With increasing depth of attack the local chromium concentration in the alloy at the base of the pit attains a critical value (∼16%) for a protective chromium oxide film to reform; the pitting attack then effectively ceases, although a a subsequent slow rate of growth continues through the protective film at the base. The observed maximum depth of pitting as a function of time is consistent with the parabolic variation predicted by the proposed mechanism. There is no significant difference in the kinetics of attack between the alloys examined.

29th HATFIELD MEMORIAL LECTURE: Ferrite

Abstract: The morphology of ferrite grains formed from austenite is first considered, then the refinement of ferrite grain size by controlled rolling as exemplified by HSLA steels. The influence of alloying elements is briefly examined, followed by a detailed discussion of the precipitation of carbides during and after the formation of ferrite. It is shown that the γ/α interfaces are preferred sites for the precipitation of alloy carbides (interphase precipitation), which occurs on both planar and curved boundaries. In the former, the precipitation is associated with the movement of small ledges across the γ/α interface, whereas the curved bands of precipitate are formed on high-energy boundaries which move by bowing around the particles. A change in the nature of the γ/α interface often leads to fibrous carbide growth, while more rapid rates of cooling lead to the formation of supersaturated ferrite and subsequent precipitation of carbides on dislocations. The dislocations in the ferrite are shown to play...

High melting point process for Au:Sn:80:20 brazing alloy for chip carriers

Abstract: Brazing of elements to electronic chip carrying substrates requires brazing materials strong at high temperatures used to remove and replace chips. Flanges and pins are brazed with Au:Sn brazing alloys modified during brazing by addition of Group IB metal to the brazing material to promote formation of the higher melting point β phase of the alloy and a Group VIII metal to draw Sn out of the melt by gettering, also to promote formation of the β phase of the alloy and to thicken the braze material. An Au preform is plated with Ni and juxtaposed with surfaces to be brazed and the brazing materials to add Ni and Au to the melt almost simultaneously.

Thermal processing of ferritic 5Mn steel for toughness at cryogenic temperatures

Abstract: It is shown that a thermal treatment which combines grain refinement with an intercritical temper (the 2BT treatment) may be used to achieve a promising combination of strength and toughness in a nickel-free ferritic steel of nominal composition Fe-5Mn-0.2Mo-0.04C at temperatures as low as -196 °C. The properties achieved are attributed to a symbiotic influence between the grain refinement treatment and the introduction of thermally stable retained austenite during intercritical tempering, a conclusion supported by a comparison of the results to those obtained with simpler heat treatments. The influence of carbon, manganese, and nickel additions to the base compositions are studied. An increase in carbon content above 0.04 wt pct causes a deterioration in toughness, as does an increase in manganese to 8 wt pct. An addition of 1 to 3 wt pct nickel is beneficial giving an increase in alloy strength at -196 °C without loss of toughness.

Surface segregation of a Pt–Au alloy: An atom‐probe field ion microscope investigation

Abstract: An absolute composition depth profile of a dilute gold alloy of platinum is obtained with a true atomic layer depth resolution. At 600±20 °C, the top {001} layer Au concentration is found to be as high as 99±20% for a sample with a bulk gold concentration of 4.1±0.7%. The Au concentration decreases monotonically into the bulk, with a characteristic depth of about three atomic layers.