Showing papers on "Tensile testing published in 2019"

In-situ TiB/Ti-6Al-4V composites with a tailored architecture produced by hot isostatic pressing: Microstructure evolution, enhanced tensile properties and strengthening mechanisms

Abstract: In-situ synthesized titanium borides reinforced Ti-6Al-4V composites with a tailored reinforcement architecture were successfully prepared by hot isostatic pressing (HIP) starting from a TiB2/Ti-6Al-4V powder system. The microstructure of the composite samples was investigated using X-ray diffraction (XRD) technique and scanning electron microscopy (SEM), and the mechanical properties were evaluated through room and high temperature tensile testing. It is found that during HIP the additive particles TiB2 have totally transformed into TiB needles, which tend to decorate at prior particle boundaries of the consolidated powder particles to form a network structure. With increasing TiB2 addition from 3 wt.% to 8 wt.%, the microstructural feature of the TiB network structure experiences the variations of discontinuous TiB reinforcement → quasi-continuous TiB reinforcement → continuous TiB reinforcement. The room temperature tensile properties of the composites are improved with increasing addition of TiB2 from 3 wt.% to 5 wt.%, but the tensile strength of the sample with 8 wt.% TiB2 drastically decreases. As to the high temperature properties, the titanium boride reinforced Ti-6Al-4V alloy composites can be an increased maximum service temperature by over 200 °C while retaining the same tensile strength accompanied with a suitable elongation. The strengthening mechanism is mainly attributed to the load-bearing transformation, grain refinement and dispersion strengthening.

Ultrahigh-performance TiNi shape memory alloy by 4D printing

Abstract: For additively manufactured components, it's widely accepted to have high enough energy input to facilitate nearly full density and low enough energy input to avoid cracking tendency. In this work, ultrahigh-performance Ti 50.6 Ni 49.4 (at.%) shape memory alloy (SMA) was manufactured by selective laser melting (SLM) under high enough energy inputs (155–292 J/mm 3 ). The microstructure, phase transformation behaviors, mechanical and shape memory properties of the SLM-manufactured SMA were investigated by various characterization methods of X-ray diffraction, scanning and transmission electron microscopies, differential scanning calorimetry, room temperature and stress-controlled cyclic tensile tests, etc. Results show that the martensite content and the austenite and martensitic transformation temperatures decrease with the decrease of laser energy input (the increase of laser scanning speed). Interestingly, the SLM-manufactured SMA exhibits ultrahigh tensile strength of 776 MPa and elongation of 7.2% under room-temperature tensile condition. In addition, stress-controlled cyclic tensile tests under 400 MPa indicate that the SLM-manufactured SMA has ultrahigh shape memory effect of 98.7% recovery ratio and 4.99% recoverable strain after ten times loading-unloading cycle. The ultrahigh mechanical and shape memory properties are associated to the combined effects of dispersedly distributed nano-sized Ti 2 Ni precipitates, ultrafine grains and profuse dislocations in the SLM-manufactured SMA. This work substantiates, for the first time, high enough energy input in SLM can be applied to manufacture ultrahigh-performance TiNi SMAs.

Direct laser metal deposition of Inconel 738

Abstract: Inconel 738 is one of the widely used nickel-based superalloys in high-temperature applications, especially in land-based and aerospace gas turbine engines. This paper reports the feasibility of direct laser metal deposition (LMD) of Inconel 738. Cracks evolved during deposition at the substrate/deposit interface and within the deposit along high angle grain boundary for scanning speed of 6 and 12 mm/s due to the intense residual stress and incipient melting. Results showed liquation cracking due to low melting crack boundary γ′ and significant micro-segregation of Al and Ti along the crack boundaries. By maximizing the energy density and by reducing the scanning speed to 3 mm/s, crack-free single wall specimens were successfully manufactured. Microstructural evolution of primary, secondary, grain boundary γ′, MC carbides, and M2B borides in the as-deposited and heat-treat specimens are discussed. Mechanical properties and microstructural development were investigated using tensile testing and scanning electron microscopy. Energy dispersive spectroscopy confirmed significant micro-segregation on various elements along the interdendritic and grain boundaries. X-ray diffraction validated the presence of the observed carbides and boride in the as-deposited and heat-treated samples.

Effect of hot isostatic pressing (HIP) on microstructure and mechanical properties of Ti6Al4V alloy fabricated by cold spray additive manufacturing

Abstract: The interior porous defects formed during the layer-by-layer fabrication process have attracted increasing attention for different additive manufacturing (AM) techniques and are regarded as a crucial factor affecting the overall performance. In this work, aiming at the cold spray Ti6Al4V bulk materials, the hot isostatic pressing (HIP) treatment is adopted to reduce the interior defects, adjust the microstructure, and improve the mechanical properties. To characterize the pore morphologies and porosity evolution, the CS Ti6Al4V sample is characterized by optical microscopy and X-ray computed tomography (XCT). The 3D reconstructions by XCT show that the fully dense Ti6Al4V alloy can be obtained through the high temperature diffusion and high pressure compacting of the HIP sample. After the HIP treatment, the severely deformed grains experience an obvious growth with the uniformly distributed β precipitates around equiaxed α grains. The tensile test shows that the strength of CS Ti6Al4V alloys can be largely improved by the enhanced diffusion and resultant metallurgical bonding. With the HIP treatment, the CS samples exhibit highly densified morphology and adjusted microstructure that can benefit the improvement of mechanical properties.

Conventional and cooling assisted friction stir welding of AA6061 and AZ31B alloys

Abstract: Conventional and cooling assisted friction stir welded Al–Mg joints were investigated by visual inspection, optical macro plus microscopy, scanning electron micrographs, energy dispersive X-ray spectroscopy, X-ray diffractions, tensile testing and micro hardness indentation. The nugget zone is characterized by onion rings composed of different phases such as Mg in an Al matrix, Al in an Mg matrix as well as intermetallic compounds, Al3Mg2 and Al12Mg17. A diffusion layer was detected on the Al side of the joint between the nugget and thermo-mechanically affected zones identifying a solid solution of Mg in Al. No diffusion layer was observed on the Mg side. The tensile strength of the dissimilar joints is enhanced by cooling assisted welding process due to the reduction in the amount of intermetallic compounds inside the weld bead. Congruently, higher hardness peaks are reported in the nugget zone of conventional FSW joint with respect to the CFSW joint.

Effect of δ phase on high temperature mechanical performances of Inconel 718 fabricated with SLM process

Abstract: The paper studies comparatively on the microstructures and mechanical performances at elevated temperature of SLM-fabricated Inconel 718 alloy in as-build, SHT 980, SHT 1080, SHT 980 + 1080 heat treated conditions. The morphology and distribution of δ phase in the γ matrix are regulated by pre-designed heat treatment schemes, their effects on tensile properties and stress rupture properties at elevated temperature are discussed. The results show that the specimens of SLM-fabricated Inconel 718 alloy in SHT 980 + 1080 heat treated conditions possess the optimum mechanical performances at elevated temperature, in which the morphology and distribution of δ phase in the γ matrix are the key factors in determining their high temperature performances. The excessive δ phases within grains and along grain boundaries can easily lead to dislocation piling up in the process of tensile test at elevated temperature, causing local stress concentration and microcrack generation in the matrix, further initiating premature failure of parts. However, lack of δ phase will reduce the high temperature strength of grain boundaries and then influence the high temperature mechanical properties. As a result, the suitable heat treatment is used to regulate the precipitation of δ phase and the moderate amount of δ phases precipitate along grain boundaries, further improving high temperature mechanical properties of IN718 alloy.

Additive manufacturing of fine-grained and dislocation-populated CrMnFeCoNi high entropy alloy by laser engineered net shaping

Abstract: The equiatomic CrMnFeCoNi high entropy alloy is additively manufactured by the laser engineered net shaping (LENSTM) process, and the solidification conditions, phase formation, as-deposited microstructures, and tensile behavior are investigated. The LENSTM-deposited CrMnFeCoNi alloy exhibits a single-phase disordered face centered cubic (FCC) structure, as evidenced by X-ray diffraction (XRD), and rationalized by Scheil's solidification simulation. Furthermore, microstructures at multiple length scales, i.e. columnar grains, solidification substructures, and dislocation substructures, are formed. The tensile deformation process is mainly accommodated by dislocation activities with the assistance of deformation twinning. The tensile yield strength of the LENSTM-deposited CrMnFeCoNi alloy is comparable to that of finer-grained wrought-annealed counterparts, due to the additional initial-dislocation strengthening. However, the uniform tensile elongation, by contrast, is lowered, which is attributed to the increased dynamic dislocation recovery rate and hence the weakened work hardening capability of the LENSTM-deposited CrMnFeCoNi. This study demonstrates the capability of the LENSTM process for manufacturing the CrMnFeCoNi alloy, with high performance, for engineering applications.

Evaluation of the mechanical and wear properties of titanium produced by three different additive manufacturing methods for biomedical application

Abstract: Commercially pure titanium, as a widely used metallic biomaterial, was fabricated using dissimilar additive manufacturing (AM) methods, namely selective laser melting (SLM), laser engineered net shaping (LENS) and wire arc additive manufacturing (WAAM). Microstructures as well as mechanical and wear properties of the produced titanium samples were studied. Diverse microstructural features were related to the different linear energy densities and cooling rates induced by each AM method. Tensile testing evaluation indicated the highest yield and ultimate tensile strengths as well as elastic energy for titanium produced by SLM. However, the maximum ductility was obtained in the WAAM-fabricated titanium due to its larger grain size and slightly higher densification. All the mechanical properties obtained were either superior or comparable to those of cast and powder metallurgy produced titanium. Fracture surface analysis showed the presence of mainly coarse and fine dimples for WAAM and SLM-produced samples, respectively. This was consistent with the grain size of each sample. Wear performances and mechanisms were also examined and the results were in agreement with the values obtained from the hardness to elastic modulus ratios (H/E and H3/E2).

Analysis of tensile strength of a fused filament fabricated PLA part using an open-source 3D printer

Abstract: The application of the fused filament fabrication (FFF) or fused deposition modeling (FDM) may be limited due to relatively poor mechanical properties of the 3D-printed components. The present experimental investigation quantifies the effect of the three process parameters viz. raster angle, layer height, and raster width on the tensile properties of the FFF-printed PLA, using an open-source 3D printer. The mean effect of each process parameters on the tensile properties and the effect of the interaction are discussed. From the result analysis, it is found that raster angle, raster width, and interaction of layer height and raster width have a significant influence on the tensile properties. Tensile test results show that parts printed at 0° raster angle exhibit higher tensile strength as compared to those with 90° raster angle. Furthermore, fractography was performed on the tensile specimen using a high-precision measuring microscope to determine the effect of process variables on modes of failure. A close relationship between the raster angle and failure mode has been observed and critically discussed.

Tensile, physical and morphological properties of oil palm empty fruit bunch/sugarcane bagasse fibre reinforced phenolic hybrid composites

Abstract: Recently, agriculture residue such as oil palm empty fruit bunch (OPEFB) and sugarcane bagasse (SCB) fiber have been attracting attention to a researcher as a high potential reinforcement material for composite material in building sector. Agriculture biomass are biodegradable, sustainable, low cost and lightweight materials for composite industries. In this paper, OPEFB and SCB fiber used as filler in different ratio to fabricate hybrid composites by hand lay-up technique while maintaining total fibre loading 50 wt%. Tensile test using UTM INSTRON machine, water absorption, thickness swelling, density, void content and micrographs of hybrid composites and pure were determined. This research found that hybridization of OPEFB/SCB fiber composites indicates better performance and properties comparing with pure fiber composites. Obtained results showed that 7OPEFB:3SCB hybrid composites display highest tensile strength and modulus, 5.56 MPa and 661.MPa, respectively with less porous and voids area compared to pure composites. While 3OPEFB:7SCB hybrid composites show lower water absorption and thickness swelling after 24 h analysis. This research addresses agriculture residue seen as an alternative green product material to apply in wall as a thermal insulation and heat retention, which are important in buildings and construction sector for the purpose of energy saving.

Mechanical behaviour of fly ash/SiC particles reinforced Al-Zn alloy-based metal matrix composites fabricated by stir casting method

Abstract: In the present work Al-Zn/fly ash/SiC reinforced composites are fabricated through vortex method using stir casting route. Fly ash is abundantly available in thermal power plants which is considered to be a major industrial waste. This paper reports the microstructural evaluation and mechanical behaviour of aluminium-zinc alloy reinforced with fly ash and silicon carbide (SiC) has been investigated. Composites reinforced with fly ash and SiC in different weight percentages varying from 0 -10 wt percentage with a particle size of 53 μm were prepared. The prepared composites were characterized using optical microscope, scanning electron microscope (SEM), Electron back scattered diffraction(EBSD) and tensile testing machine. The microstructural studies revealed the presence of fly ash and SiC particulates and are distributed uniformly throughout the matrix whereas the grainsize refinement is observed in EBSD analysis. The incorporation of fly ash particles enhanced the hardness and tensile properties like ultimate tensile and yield strengths were improved by the addition of SiC particles. The strengthening mechanisms were discussed for the improved properties.

Effect of CNTs dispersion on electrical, mechanical and strain sensing properties of CNT/epoxy nanocomposites

Abstract: The remarkable electrical and mechanical properties of carbon nanotubes (CNTs) render CNT-reinforced nanocomposites as potentially attractive materials for strain-sensing and monitoring purposes. The dispersion state of CNTs in polymeric matrix has a significant role on the physical and the mechanical properties of the resulting CNT reinforced nanocomposites. In this study, a series of experiments were designed to investigate the effect of dispersion process parameters and CNT concentration, as well as their interactions on electrical, mechanical and strain sensing properties of CNT/epoxy nanocomposites. Composite samples were produced under different CNT/resin dispersion conditions based on a design of experiments approach, and were characterized using tensile testing, conductivity measurements and micrography. Based on the results, two regression models were established to predict the electric conductivity and the tensile strength of the CNT/epoxy nanocomposites. The robustness and accuracy of the models were verified by implementing verification tests. It was found that the nanocomposites fabricated by dispersing of lower amount of CNT with high mixing speeds and long mixing times had improved sensory properties and were more suitable for strain sensing applications. The effect of post dispersion state on electrical conductivity was also investigated by curing nanocomposites into a magnetic field. A straight forward 2D percolation-based model was used to predict the electrical conductivity and piezoresistivity of the magnetized nanocomposites. Both Experimental and numerical results showed that the electric conductivity could be increased significantly with post dispersing of CNTs using magnetization.

Microstructure and Properties of a Novel Cu–Ni–Co–Si–Mg Alloy with Super-high Strength and Conductivity

Abstract: The Cu–4.5Ni–1.2Co–1.0Si–0.15Mg alloy with super-high strength and high electrical conductivity was designed, and a two-step thermo-mechanical treatment was applied to improve the mechanical and electrical properties of the alloy. The microstructure and properties of the alloy were investigated by transmission electron microscope observation, tensile test, hardness and electrical conductivity measurements. The results show that the final alloy treated by two-step thermo-mechanical process has a hardness of 329 HV, a yield strength of 1086 MPa, an elongation of 3.6%, and an electrical conductivity of 30.1%IACS, respectively. The nanoscale β-Ni3Si and δ-(Co,Ni)2Si precipitates form during the thermo-mechanical process, and the addition of the Co could promote the precipitation of δ-(Co,Ni)2Si particles. The orientation relationship (OR) between Cu matrix and the precipitates is: (022)Cu//(011)β//(010)δ and [100]Cu//[100]β//[001]δ. Comparing with the directly aging treatment and one step thermo-mechanical treatment, precipitates that form during the two-step thermo-mechanical process are much smaller and distributed more densely, resulting in the better comprehensive properties of the alloy.

Controlling martensitic decomposition during selective laser melting to achieve best ductility in high strength Ti-6Al-4V

Abstract: Systematic variations of the exposure time and point distance of the pulsed laser used in selective laser melting (SLM) of Ti-6Al-4V resulted in three representative microstructures: the fully martensitic α', the near-α' containing a small amount of isolated β, and the fully lamellar α/β. The energy density in SLM determines the steady-state temperature in a deposited layer reached by balance between heat input from the subsequent layers and heat loss into the previous ones. A critical energy density was revealed below which no in-situ α' decomposition occurred. On the other hand, the in-situ formation of fully lamellar α/β was obtained using energy density higher than this critical value, leading to a steady-state temperature above that for α' decomposition for a sufficiently long duration. All three microstructures exhibited high tensile yield strength of 1100–1150 MPa, with excellent tensile elongation in the fully martensitic α' (~15%) and fully lamellar α/β (~12%) but significantly lower ductility in the near-α' (

Mechanical properties of high ductile magnesium oxychloride cement-based composites after water soaking

Abstract: Applications of magnesium oxychloride cement-based concrete in civil engineering are limited due to material's poor water resistance and inherent brittleness. For improvement, a new kind of material, magnesium oxychloride cement-based engineered cementitious composite (MOC-ECC), was developed. This paper introduces the effects of fly ash and polyethylene fibers incorporations on the fluidity, tensile behavior and compressive properties of MOC-ECC. The test results indicated that MOC-ECC exhibits outstanding strain hardening and multi-cracking characteristics with tensile strain capacity up to 8% and tensile strength over 7 MPa. More importantly, to explore the combined influences of fly ash and polyethylene fiber on the water resistance of MOC-ECC, XRD and SEM were used to analyze the variations of chemical composition and microstructure, and three-point bending test and single crack tension test were conducted to obtain the fracture toughness and fiber bridging capacity, respectively. An explanation to the mechanisms of the enhanced mechanical property and water resistance is presented at microscopic and mesoscopic scales.