High temperature wear performance of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy subjected to laser shock peening

This paper investigates the influence of laser shock peening (LSP) parameters on surface integrities and high temperature wear performances of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy. Surface integrities include surface roughness, residual stress and micro-hardness are measured. High temperature wear performance of TC11 alloy with and without LSP are investigated. The results indicate that multiple LSP impacts can improve surface micro-hardness and induce compressive residual stress in the surface layer. Moreover, the friction coefficient and wear rate of TC11 alloy significantly decrease after LSP with optimised parameters. The improved wear performance is ascribed to the low surface roughness, higher surface micro-hardness and compressive residual stress induced by multiple LSP impacts in the surface layer.     

Study of the dynamic recrystallization of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy in β-forging process via Finite Element Method modeling and microstructure characterization

By integrating the thermomechanically coupled simulation with the mathematically modeling of microstructure evolution using Finite Element Method (FEM), the study of the dynamic recrystallization (DRX) of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy in β-forging process is conducted. Through physical experiment, microstructure characterization and FEM-based microstructure modeling, the DRX behavior of the Ti-alloy in β-forging process is extensively explored. The effects of plastic deformation strain, strain rate and deformation temperature on the DRX of the Ti-alloy in terms of DRX volume fraction, DRX grain size and the average grain size are systematically investigated. The simulation results show that the increase of plastic deformation strain, deformation temperature, and strain rate contributes to the DRX of the alloy. The simulation and experimental results further reveal that the FEM-based microstructure evolution modeling is able to predict the DRX behavior and the microstructure evolution of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy in β-forging process.     

Microstructure and mechanical properties of Al–Si cast alloy with additions of Zr–V–Ti

The microstructure and tensile properties at temperatures up to 300 °C of an experimental Al–7Si–1Cu–0.5Mg (wt.%) cast alloy with additions of Ti, V and Zr were assessed and compared with those of the commercial A380 grade. The microstructure of both alloys consisted of Al dendrites surrounded by Al–Si eutectic containing, within its structure, the ternary Al–Al₂Cu–Si phase. Whereas the Al₁₅(FeCrMn)₃Si₂ phases were present in the A380 alloy, Ti/Zr/V together with Al and Si phases, Al(ZrTiV)Si, were identified in the experimental alloy. As a result of chemistry modification the experimental alloy achieved from 20% to 40% higher strength and from 1.5 to 5 times higher ductility than the A380 reference grade. The role of chemistry in improving the alloy thermal stability is discussed.     

Microstructure and mechanical properties of wire arc additive repairing Ti–6.5Al–2Sn–2Zr–4Mo–4Cr titanium alloy

Wire arc additive manufacture (WAAM) technology was employed to repair Ti–6.5Al–2Sn–2Zr–4Mo–4Cr (TC17) titanium alloy, which is widely used as compressor blades and blisk. The microstructure evolution and mechanical properties of the repaired specimen were investigated. The results show that the repaired specimen has a good verticality, and it forms good metallurgical bonding with the base metal. The ultimate strength of the interface specimen can reach 88.2% of the base metal. The elongation is slightly lower than the base metal due to the fact that half of the tensile interface specimens with little deformation are base material. Therefore, WAAM technology might be a potential and economical method to repair damaged blade by optimising the WAAM process.     

The synergic effects of Sc and Zr on the microstructure and mechanical properties of Al–Si–Mg alloy

In order to clarify the possibility of Zr substitution for Sc on the modification of Al-Si casting alloys, the microstructural evolution and tensile properties of Al-Si-Mg based alloys with different combinations of Sc and Zr contents (Sc + Zr = 0.5 wt.%) were systematically investigated. It was found that 0.5 wt.% Sc addition could refine the microstructure significantly and modify the eutectic Si from plate-like morphology to fiber, which promotes the spheroidization of eutectic Si during heat treatment. When Zr was added to partly replace Sc, the microstructure was first further refined, but was then slightly coarsened with increasing Zr content. Moreover, high Zr content was found to decrease its modification on eutectic Si. It was observed that Zr can also concomitantly improve strength and ductility compared with the alloy modified by Sc only. The improvement of mechanical properties was attributed to microstructural refinement, particularly the modification of eutectic Si and precipitation of secondary nano-scale Al₃(Sc_1 − xZr_x) dispersoids.     

Sc and Sc–Zr effects on microstructure and mechanical properties of Be–Al alloy

Herein, we investigated the effects of Sc and Sc–Zr on the microstructure and mechanical properties of Be–Al alloy, showing that Sc alloying resulted in Be grain refinement and reduced the secondary dendritic arm spacing (SDAS) of these grains by 1/3, whereas Sc–Zr alloying further decreased the SDAS to 7.5?µm and afforded equiaxed/cellular-like morphology with further refined Be grains. The above alloying resulted in the formation of intermetallic compounds (Be₁₃Sc, Be₁₃Zr, and Al₃(Sc_1–xZr_x)), increasing the macrohardness of the Be–Al alloy, with the microhardness and elastic modulus of the Be phase increasing to a larger extent than those of Al. Importantly, Sc–Zr alloying resulted in better microstructure modification and mechanical reinforcement than Sc alloying.     

Evaluating the microstructure and mechanical properties of friction stir processed Al–Si alloy

In this study, mechanical behaviour and microstructural evolution in friction stir processing (FSP) of casting hypereutectic A390 aluminium alloy have been investigated. The mechanical behaviour of FSP samples was investigated by measuring the strain rate sensitivity using shear punch testing. The room-temperature shear punch tests were conducted at shear strain rates in the range of 10^?4–10^?1?s^?1. The results indicate that the strain rate sensitivity index increases from about 0.015 to 0.120 for as-cast A390 after third FSP pass and then experiences a further growth in FSP passes. The increase in the grain size and CuAl₂ intermetallic particle size result in a reduction in strain sensitivity index as well as shear strength after third FSP pass.     

Texture and microstructure characterization in laser additive manufactured Ti–6Al–2Zr–2Sn–3Mo–1.5Cr–2Nb titanium alloy

Laser additive manufacturing (LAM) is a novel manufacturing technique in which metal components can be fabricated layer by layer. In this study, a recently developed damage tolerance titanium alloy TC21 (Ti–6Al–2Zr–2Sn–3Mo–1.5Cr–2Nb) was deposited by LAM process. Texture and microstructure characterization have been investigated by XRD, SEM and EBSD. Prior β grains texture analysis indicates that the (100) poles concentrate in build direction with a texture intensity about 18.7. During cooling down from β phase field, the β to α phase transformation follows the Burger orientation relationship and a pronounced variant selection occurred. Besides, morphology and scale of α phase are quite different along the build direction due to different thermal history. Very fine rib-like α phase with the length less than 2 μm and acicular martensite α' can be obtained at the bottom and the top of the sample, respectively. In the middle position, distribution and morphology of α phase is quite uneven and the precipitation sequence of α phase is α_GB → α_WGB → α_WM → α_S. The reasons by which they formed are discussed.     

Influence of oxygen content on microstructure and mechanical properties of Ti–Nb–Ta–Zr alloy

The influence of oxygen content on microstructure and mechanical properties of Ti–22.5Nb–0.7Ta–2Zr (at.%) alloy was investigated in this work. According to experiments, the grains were refined apparently when the oxygen content was between 1.5% and 2.0%. The ultimate tensile strength (UTS) increased and elongation decreased with increasing oxygen content. But at the content of 1.0%, the elongation was nearly the same to that of the original alloy (about 16%). The elastic modulus remained comparatively low (<65 GPa) when the content was lower than 1.5%, and then increased dramatically. Therefore, there existed the best oxygen content-1.0%, at which fine grains were obtained, as well as UTS of 750 MPa, elongation of 16% and elastic modulus of 65 GPa. The Ti–22.5Nb–0.7Ta–2Zr–1.0O alloy maintained typical ductile fracture characteristics of beta titanium alloy, and had a little superelasticity.     

Atomic bonding and mechanical properties of Al–Li–Zr alloy

The atomic bonding of Al–Li alloy with minor Zr is calculated according to the “Empirical Electronic Theory in Solids”. The result shows that the stronger interaction between Al and Zr atoms, which leads to form the Al–Zr segregation regions, promotes the precipitation of Al₃Zr particles and produces a remarkable refinement of Al₃Li grains in the alloy. Because there are the strongest covalent Al–Zr bonds in Al₃Zr and Al₃(Zr, Li) particles, these covalent bonds can cause a great resistance for dislocation movement, and is favorable to strengthen the alloy. On the other hand, with precipitating the Al₃(Zr, Li) particles, it causes the coherent interphase boundary energy of Al/Al₃Li to decrease, and atomic bonding is well matched in between the interface of two phases.     

Processing and mechanical properties of porous Ti–7.5Mo alloy

Titanium (Ti) and its alloys continue to be utilized extensively for skeletal repair and dental implants. Most metallic implant materials including pure Ti and Ti alloys used today are in their solid forms and are often much stiffer than human bone. However, the elastic modulus of Ti and Ti alloys can be reduced through the introduction of a porous structure, which may also provide new bone tissue integration and vascularization abilities. In the present study, porous Ti–7.5Mo alloy scaffolds made from ball-milled alloy particles and sintered at 1100 °C for 10, 15 and 20 h respectively were successfully prepared through a space-holder sintering method. In the sintered Ti–7.5Mo, no obvious diffraction peaks of elemental Mo remained after the sintering, and a duplex α + β microstructure was confirmed from the XRD pattern. The samples made from BM15 (the alloy particles ball-milled for 15 h) had higher relative density, compressive strength and elastic modulus performance than those from BM3 and BM30 (the alloy particles ball-milled for 3 and 30 h, respectively) when they were sintered under the same conditions. Moreover, the longer sintering time lead to the higher relative density and the greater compressive strength and modulus of the sample. In this work, the strength and modulus of the sintered porous Ti–7.5Mo conforms to the basic mechanical property requirement of cancellous bones.     

Effect of predeformation on microstructure and mechanical properties of Al–Cu–Li–Zr alloy containing Sc

Abstract

The effects of prior cold deformation on the microstructures and the room temperature mechanical properties of an Al–3·5Cu–1·5Li–0·22(Sc + Zr) alloy have been observed by using TEM and tensile test at room temperature. The results show that the alloy has the character of aging hardening, and the major phase of precipitation and strengthening is T₁ phase. The result also show that prior cold deformation leads to more dispersive and uniform distribution of T₁ precipitations. It accelerates aging response, causes earlier aging peak occurrence, and enhances strength greatly. However, the plasticity of the alloy is declined with prior cold deformation. In contrast, excessive prior cold deformation causes coarsening and heterogeneous distribution of T₁ phase. It also reduces the strength of the alloy, therefore, influences the composite properties of the alloy. The favourable prior cold deformation is about 3·5% under the experimental condition.     

Influence of solutionising and aging temperatures on microstructure and mechanical properties of cast Al–Si–Cu alloy

Abstract

This paper presents the influence of solution and aging temperatures on the microstructure and mechanical properties of 319 secondary cast aluminium alloy. Experimental alloy was subjected to different heat treatment cycles. Heat treatments were designed with two solutionising temperatures (504 and 545°C) at two solutionising times (4 and 8 h), followed by quenching in water at 60°C and artificial aging. The artificial aging was carried out at two temperatures (200 and 154°C) for 6 h. The improvement in mechanical properties was obtained with low solution temperature (504°C) for 8 h followed by quenching in water to 60°C and aging at low temperature (154°C). The increase in the solutionising temperature from 504 to 545°C was recommendable only for short solutionising time (4 h). Increase in the aging temperature from 154 to 200°C has led to the increase in hardness with the corresponding decrease in ductility. Aging under unfavourable conditions (prolonged aging at high temperature) caused coarsening of spheroidised eutectic silicon crystals and precipitated particles resulted in deleterious effect on the tensile strength.     

Evolution of microstructure and mechanical properties during quenching and tempering of ultrahigh strength 0.3C Si–Mn–Cr–Mo low alloy steel

Effects of quenching and tempering treatments on the development of microstructure and mechanical properties of ultrahigh strength 0.3C Si–Mn–Cr–Mo low alloy steel were investigated. Samples were austenitized at 1123–1323 K for 2400 s and oil quenched (OQ) to produce mixed microstructures. Tempering was carried out at 473–773 K for 2–3 h. Phase transformation temperatures were measured using dilatometer. The microstructures were characterized using optical and scanning electron microscope. SEM–EDS analysis was carried out to determine the type and size of non-metallic inclusions. Volume percent of retained austenite was measured by X-ray diffraction technique. Hardness, tensile properties, and impact energies were also determined for all heat treated conditions. Fractography of impact specimens were done using stereomicroscope and SEM. The results showed that newly developed steel exhibited peak hardness, yield strength, and tensile strength of about 600 HV, 1760 MPa, and 1900 MPa, respectively, when OQ from 1203 K and tempered in between 473 and 573 K, combined with adequate ductility and impact toughness. Decrease in hardness and strength was observed with increasing tempering temperature whereas the impact energy was stable up to 623 K, however, impact energy was found to decrease above 632 K due to temper martensite embrittlement.     

Effects of Cu content on microstructure and mechanical properties of Al–14.5Si–0.5Mg alloy

This study elucidates how Cu content affects the microstructure and mechanical properties of Al–14.5Si–0.5Mg alloy, by adding 4.65 wt.% and 0.52 wt.% Cu. Different Fe-bearing phases were found in the two alloys. The acicular β-Al₅FeSi was found only in the high-Cu alloy. In the low-Cu alloy, Al₈Mg₃FeSi₆ was the Fe-bearing phase. Tensile testing indicated that the low-Cu alloy containing Al₈Mg₃FeSi₆ had higher UTS and elongation than the high-Cu alloy containing the acicular β-Al₅FeSi. It is believed that the presence of the acicular β-Al₅FeSi in the high-Cu alloy increased the number of crack initiators and brittleness of the alloy. Increasing Cu content in the Al–14.5Si–0.5Mg alloy also promoted solution hardening and precipitation hardening under as-quenched and aging conditions, respectively. The hardness of the high-Cu alloy therefore exceeded that of low-Cu alloy.     

Effect of Si content on microstructure and mechanical properties of Al–Si–Mg alloys

Microstructure and mechanical properties of as-cast and as-extruded Al–Si–Mg alloys with different Si content are investigated by tensile test, microstructure observation. High density of Si particles in the Al alloys can induce dynamic recrystallization during hot extrusion and it becomes more matured with an increase in the density of Si particles. The tensile strength of as-cast and as-extruded alloys can be improved with the increase of Si content and hot extrusion make the elongation of alloys increase dramatically. Considerable grain refining effect caused by recrystallization occurred during hot extrusion of S2 (equivalently commercial A356 alloy) and S3 (near eutectic alloy) alloys plays an important role in the improvement of elongation. A good combination of strength and elongation for the as-extruded S3 alloy indicates that near eutectic Al–Si alloys can be hot-extruded to produce aluminum profiles with high performance.     

Characterization of microstructure and mechanical properties of Al–Cu–Mg–Ag–(Mn/Zr) alloy with high Cu:Mg

This study examines the effects of the addition of Mn or Zr on the microstructure and mechanical properties of Al–Cu–Mg–Ag alloy using optical microscopy, scanning electron microscopy, X-ray diffraction, differential scanning calorimetry, transmission electron microscopy, tensile test, and tear test. The results showed that the alloy with Zr exhibited the highest strength and the lowest fracture toughness, which may be attributed to the segregation of the secondary phases containing the Zr element on the recrystallization grain boundaries. The alloy with Mn exhibited strength that is roughly equal to the Al–Cu–Mg–Ag alloy and the highest fracture toughness, which may be due to the formation of secondary phases containing Mn and Fe elements. Mn or Zr addition also has no remarkable influence on the characteristics of the precipitates. The Ω phase and a small quantity of θ′ phases dominated the microstructure of the three alloys after aging.     

Effects of Si addition on microstructure and mechanical properties of Mg–8Gd–4Y–Nd–Zr alloy

Effects of Si addition (1.0 wt.%) on microstructure and mechanical properties of Mg–8Gd–4Y–Nd–Zr alloy have been investigated using scanning electron microscopy (SEM) equipped with energy dispersive spectrum (EDS), X-ray diffraction (XRD), hardness measurements and tensile testing. The results indicated that the addition of Si led to the formation of Mg₂Si and (RE + Si)-rich particles, which enhanced the Young’s modulus of the alloy by 7 GPa while decreased the yield strength and ultimate strength by 10 MPa and 31 MPa, respectively. The tensile properties of the Mg–8Gd–4Y–Nd–Zr–Si alloy are as follows: Young’s modulus E = 51 GPa, yield strength σ_0.2 = 347 MPa, ultimate strength σ_b = 392 MPa and elongation δ = 2.7%. The increase in Young’s modulus was attributed to the formation of particles with high Young’s modulus, while the decrease in strength was ascribed to the decrease in volume fraction of metastable β′ precipitates caused by the consumption of rare earth atoms due to the formation of the rare earth containing particles.