Effect of heat treatment and exposure on microstructure and mechanical properties of Ti–25V–15Cr–2Al–0.2C (wt%)

The effect of heat treatment and exposure on the microstructure and mechanical properties of extruded, burn-resistant β titanium alloy Ti–25V–15Cr–2Al–0.2C (wt%) has been studied. It has been found that pre-exposure annealing at 600, 700 and 800°C affected the distribution of α phase that precipitated following subsequent exposure at temperatures between 450 and 550°C. Samples annealed at 600°C and subsequently exposed at 450°C showed excellent microstructural and property stability. Although the room-temperature ductility of the alloy decreased and the strength increased slightly with increasing exposure time at 500°C, no further drop in ductility was observed after 500 h. However, a gradual degradation of properties with exposure time was observed in samples exposed at 550°C. The significance of the observations is discussed in terms of the effect of pre-exposure annealing and exposure on α precipitation and tensile properties.     

Effect of Ru additions on microstructure and mechanical properties of Cr–TaCr2 alloys

Early work indicated that Ru reduced the ductile-to-brittle transition temperature of Cr even at small concentrations. To evaluate the potential of Ru as a beneficial alloying element in the two-phase Cr–TaCr₂ alloys, a number of Cr–8 at.%Ta alloys with 0–10 at.%Ru were prepared, and their microstructures and mechanical properties were evaluated. The Ru addition was found to move the eutectic point of Cr–TaCr₂ to a higher Ta level, as compared to the binary Cr–Ta system. Ru partitioned preferentially in the Laves phase over in the Cr matrix, with a partitioning ratio of 2–5:1, depending on the Ru addition level. Ru was also found to mainly occupy the Cr site in the TaCr₂ Laves phase. The hardness of both the primary Cr matrix and the eutectic microconstituent increased slightly with the increase in Ru addition. At a higher Ru addition level (i.e. 10 at.%), the hardness of the primary Cr matrix increased significantly, probably due to the precipitation of extremely fine Laves-phase precipitates. The Ru addition did not noticeably affect the fracture toughness of the two-phase alloys.     

Effect of interlayer on microstructure and mechanical properties of Al–Ti ultrasonic welds

Joints of Al6061 and Ti6Al4?V alloys with pure Al-particle interlayers were conducted using ultrasonic spot welding. The microstructure, hardness, lap shear strength and fracture energy were measured for different welding energies. With increasing welding energy delivered through the sonotrode, the lap shear strength of the joints increased, reaching about 106?MPa at a welding energy of 1100?J, at which failure occurred in the pull-out mode. In the weld region, the hardness of Al6061 alloy increased with increasing weld energy, whereas the hardness of Ti6Al4?V did not change discernibly. No brittle intermetallic compounds were observed in the joints. Moreover, two simple mechanisms were described for the formation of ultrasonic spot-welded Al–Ti joints with and without the pure Al interlayer.     

Effect of Si addition on microstructure and mechanical properties of Ti–Al–N coating

Ti–Al–N coatings are widely used to prevent the untimely consumption of cutting tools exposed to wear. Increasing requirements on high speed and dry cutting application open up new demands on the quality of wear-protective quaternary or multinary Ti–Al–N based coating materials. Here, we investigated the microstructure and mechanical properties of Ti–Al–N and Ti–Al–Si–N coatings deposited on cemented carbide by cathodic arc evaporation. The formation of nanocomposite nc-TiAlN/a-Si₃N₄ structure by incorporation of Si into Ti–Al–N coating causes a significant increase on hardness from ∼ 35.7 GPa of Ti–Al–N to ∼ 42.4 GPa of Ti–Al–Si–N. Both coatings behave age-hardening during thermal annealing, however Ti–Al–Si–N coating reveal better thermal stability. Therefore, the improved cutting performance of Ti–Al–Si–N coated inserts is obtained compared to Ti–Al–N coated inserts.     

Effect of carbon addition on microstructure and mechanical properties of Ti-based bulk metallic glass forming alloys

A kind of novel Ti-based composites was developed by introducing different amounts of carbon element to the Ti50 Cu23 Ni20 Sn7 bulk metallic glass forming alloys. The thermal stability and microstructural evolution of the composites were investigated. Room temperature compression tests reveal that the composite samples with 1% and 3% （mass fraction） carbon additions have higher fracture strength and obvious plastic strain of 2 195 MPa, 3. 1% and 1 913 MPa, 1.3% respectively, compared with those of the corresponding carbon-free Ti50 Ni20 Cu23 Sn7 alloys. The deformation mechanisms of the composites with improved mechanical properties were also discussed.     

Effect of minor Zr and Sc on microstructures and mechanical properties of Al–Mg–Si–Cu–Cr–V alloys

The effects of minor contents of Zr and Sc on the microstructures and mechanical properties of Al–Mg–Si–Cu–Cr–V alloy were studied. The results show that the effects of minor Zr and Sc on the as-cast grain refinement in the ingots, the improvement in the strength of the as-extruded alloys and the restriction of high angle grain boundaries in the aged alloys can be sorted as Al₃Sc>Al₃(Zr,Sc)>Al₃Zr. None of them could stop the nucleation of recrystallization, but Al₃(Zr,Sc) phase is a more effective inhibitor of dislocation movement compared to Al₃Sc in the aged alloys. Compared with the mechanical properties of the aged alloy added only 0.15% Sc, the joint addition of Zr and Sc to the alloy leads to a very slight decrease in strength with even no cost of ductility. Taking both the production cost and the little bad influence on mechanical properties into consideration, an optimal content of Zr and Sc in the Al–Mg–Si–Cu–Cr–V alloy to substitute 0.15% Sc is 0.13% Zr+0.03% Sc.     

Effect of Al addition on microstructure and mechanical properties of Mg−Gd−Zn alloys

The microstructure evolution and mechanical properties of Mg?15.3Gd?1Zn alloys with different Al contents (0, 0.4, 0.7 and 1.0 wt.%) were investigated. Microstructural analysis indicates that the addition of 0.4 wt.% Al facilitates the formation of 18R-LPSO phase (Mg₁₂Gd(Al, Zn)) in the Mg?Gd?Zn alloy. The contents of Al₁₁Gd₃ and Al₂Gd increase with the increase of Al content, while the content of (Mg, Zn)₃Gd decreases. After homogenization treatment, (Mg, Zn)₃Gd, 18R-LPSO and some Al₁₁Gd₃ phases are transformed into the high-temperature stable 14H-LPSO phases. The particulate Al?Gd phases can stimulate the nucleation of dynamic recrystallization by the particle simulated nucleation (PSN) mechanism. The tensile strength of the as-rolled alloys is improved remarkably due to the grain refinement and the fiber-like reinforcement of LPSO phase. The precipitation of the β′ phase in the peak-aged alloys can significantly improve the strength. The peak-aged alloy containing 0.4 wt.% Al achieves excellent mechanical properties and the UTS, YS and elongation are 458 MPa, 375 MPa and 6.2%, respectively.     

Solidification behaviour,microstructure and mechanical properties of high Fe-containing Al–Si–V alloys

The paper deals with effect of Fe on the solidification behaviour and mechanical properties of unmodified and modified Al–V–Si alloys. Effect of thermo-mechanical processing on the mechanical properties of these alloys was also reported. The solidification proceeds through several invariant reactions, the first one corresponds to formation of Al₃(Fe,V,Si)-type phase. Modification with Ni–Mg master alloy changes the morphology, size and distribution of the primary as well as interdendritic phases. The modified alloys show an increase in first invariant reaction temperature and decrease in final invariant reaction temperature when compared with unmodified alloy, probably due to action of phase modification. In comparison to untreatable alloy, appreciable improvement in mechanical properties occurs on modification by Ni–Mg treatment. Hot rolling further improves the mechanical properties of the alloy.     

Effect of HfB2 on microstructure and mechanical properties of ZrB2–SiC-based composites

In this work, ZrB₂–SiC-based composites with different additives were sintered in different temperature (1600, 1700, 1800 and 1900), time (4, 8, 12 and 16) and pressure (10, 20, 30 and 40 MPa). The effect of HfB₂ (0, 5, 10, 15 vol.%) on ZrB₂-based ceramics was investigated. Microstructure evaluation and phases were done by SEM and EDAX. Effect of SPS conditions (temperature, time and pressure) on microstructure was investigated. The results showed that Hf and Zr diffuse in each other and (Zr, Hf)B₂ solid solution will be formed. In addition, it was concluded that by increasing temperature and time, solid solution formation increases. Pressure has little effect on diffusion. Also, MoSi₂ and ZrB₂ form (Zr, Mo)B₂ solid solution. Finally it is cleared that HfB₂ increases open porosity percent slightly. Finally, it was observed that HfB₂ has negative effect on densification while improves flexural strength due to (Zr, Hf)B₂ solid solution.     

Effect of microstructure on tensile properties and fracture behavior of intermetallic Ti2AlNb alloys

The tensile properties and fracture behaviors of Ti-22Al-27Nb and Ti-22Al-20Nb-7Ta alloys were investigated in the temperature range of 25-800℃ Three typical microstructures were obtained by ifferent thermomechanical processing techniques.The results indicate that the duplex microstructure has an optimum combination of tensile yield strength and ductility both at room and elevated temperatures.Adding Ta to Ti2AlNb alloy can improve the yield strength,especially at high temperature while retain a good ductility.The study on crack initiation and propagation in dedformed microstructure of Ti2AlNb alloys indicates that microstructure has ikmportant effect on the tensile fracture mechanism of the alloys.The cracks initiate within primary O/α2 grains along O/B2 boundaries or O phase laths in B2 matrix,and propagate along primary B2 grain boundaries for the duplex microstructure.The fracture mode is transgranular with ductile dimples for the duplex and the equiaxed microstructures,but intergranular for the lath microstructure.     

Effect of cerium on microstructure and mechanical properties of Sn-Ag-Cu system lead-free solder alloys

The melting point, spreading property, mechanical properties and microstructures of Sn-3.0Ag-2.8Cu solder alloys added with micro-variable-Ce were studied by means of optical microscopy, scanning electron microscopy（SEM） and energy dispersive X-ray（EDX）. The results indicate that the melting point of Sn-3.0Ag-2.8Cu solder is enhanced by Ce addition; a small amount of Ce will remarkably prolong the creep-rupture life of Sn-3.0Ag-2.8Cu solder joint at room temperature, especially when the content of Ce is 0.1%, the creep-rupture life will be 9 times or more than that of the solder joint without Ce addition; the elongation of Sn-3.0Ag-2.SCu solder is also obviously improved even up to 15.7%. In sum, the optimum content of Ce is within 0.05%-0.1%.     

Effect of carbon on microstructure and mechanical properties of DD99 single crystal superalloy

The effects of carbon on the microstructure and mechanical properties of DD99 single crystal superalloy were investigated. The results show that stress rupture life of DD99 alloy possesses peak value at carbon content of 0.03%（mass fraction）. As carbon addition is greater than 0.03%, the stress-rupture life decreases with the increase of carbon content. The tensile strength and yield strength of DD99 alloy reach peak value at 0.08% carbon and 760 ℃. On the contrary, the tensile strength and yield strength have minimal values at 0.08% carbon and 900℃. The tensile ductility of DD99 alloy basically decreases with the increase of carbon content at 760 ℃ or 900 ℃. The amount of carbides greatly increases with the addition of carbon content. Dislocation moving is retarded by carbides so that dislocation networks are apt to form, which has an important role on the mechanical properties in DD99 single crystal superalloy.     

Effect of composing element on microstructure and mechanical properties in Mo–Nb–Hf–Zr–Ti multi-principle component alloys

A series of non-equiatomic Mo–Nb–Hf–Zr–Ti alloys are synthesized to investigate the effects of the concentration variation of each composing elements on the microstructure and mechanical properties. It is found that all studied alloys form single body-centered-cubic (BCC) phase only with the variation of the lattice parameter, which indicates that the concentration variation of each composing elements has no effect on the phase constitutes. All studied alloys exhibit typically dendritic and interdendritic structure while the concentration variation of each composing elements has different effects on the microsegregation. The concentration variation of Zr leads to the most serious microsegregation. Elements with a higher melting point such as Mo and Nb solidify preferentially and thus are enriched in the dendrites. Both the increase and decrease of the concentration of each composing element reduce the hardness and strength of non-equiatomic Mo–Nb–Hf–Zr–Ti alloys compared with the equiatomic MoNbHfZrTi alloy.     

Effects of predeformation and semi-solid processing on microstructure and mechanical properties of Cr–V–Mo steel

An energy-efficient process route for manufacturing machine tools and dies of high quality was proposed based on recrystallization and partial melting (RAP) method and semi-solid forming technology. To verify its feasibility, the effects of parameters such as predeformation, heating rate, and holding time on the microstructure and mechanical properties of cast Cr–V–Mo steel were studied experimentally. Recrystallization, austenization, grain growth and partial melting occur during heating of predeformed cast billet. These behaviors refine the microstructure and improve the mechanical properties. The refinement of microstructure and improvement of mechanical properties become more significant, when RAP is conducted with larger predeformation (50%), higher heating rate (50 °C/s) and shorter isothermal holding time (20 s).     

Effects of ultrasonic vibration and manganese on microstructure and mechanical properties of hypereutectic Al–Si alloys with 2%Fe

The effects of ultrasonic vibration (USV) on the microstructure and mechanical properties of Al–17Si–2Fe–2Cu–1Ni (mass %) alloys with 0.4% or 0.8% Mn were studied. The results show that the average grain size of primary Si in the alloys treated by USV could be refined to 21–24 μm, whether with or without P modification. The P addition has no further refinement effect on the primary Si in the case of the combined use of USV with P addition. Without USV, the alloy with 0.4%Mn contains a large amount of long needle-like β-Al₅(Fe,Mn)Si phase and coarse plate-like δ-Al₄(Fe,Mn)Si₂ phase. Besides, the alloy with 0.8% Mn contains a small amount of coarse dendritic α-Al₁₅(Fe,Mn)₃Si₂ phase. With USV treatment, the Fe-containing compounds in the alloys are refined and exist mainly as δ-Al₄(Fe,Mn)Si₂ particles with average grain size of about 18 μm, and only a small amount of β-Al₅(Fe,Mn)Si phase is remained. With USV treatment and without P modification, the ultimate tensile strengths (UTS) of the alloys containing 0.4% and 0.8% Mn are 271 MPa and 289 MPa respectively at room temperature, and the UTS are 127 MPa and 132 MPa at 350 °C. The Brinell hardness of the alloys are 131 HB and 139 HB respectively. It is considered that the modified morphology and uniform distribution of the Fe-containing intermetallic compounds and the primary Si phases, which are caused by USV process, are the main reasons for the increase of the tensile strength and hardness of these two alloys.     

Effect of Y on microstructure evolution and mechanical properties of Mg−4Li−3Al alloys

To obtain magnesium alloys with a low density and improved mechanical properties, Y element was added into Mg−4Li−3Al (wt.%) alloys, and the effect of Y content on microstructure evolution and mechanical properties was investigated by using optical microscopy, scanning electron microscopy and tensile tests. The results show that mechanical properties of as-cast Mg−4Li−3Al alloys with Y addition are significantly improved as a result of hot extrusion. The best comprehensive mechanical properties are obtained in hot-extruded Mg−4Li−3Al−1.5Y alloy, which possesses high ultimate tensile strength (UTS=248 MPa) and elongation (δ=27%). The improvement of mechanical properties of hot-extruded Mg−4Li−3Al−1.5Y alloy was mainly attributed to combined effects of grain refinement, solid solution strengthening and precipitation strengthening.     

Influence of Al on the microstructure and mechanical properties of Cr–Zr–(Al–)N coatings with low and high Zr content

Low Zr (S1) and high Zr (S2) quaternary Cr–Zr–(Al–)N coatings with increasing Al content were deposited by d.c. reactive magnetron sputtering. The structure, fracture cross-section morphology and mechanical properties of the coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), nanoindentation, scratch testing and Vickers micro-indentation testing. All the coatings present an fcc NaCl-type B1 structure; in the low Zr content coatings, the diffraction peaks shift towards higher angles as the Al content increases. The grain size is approximately constant in a range from 6 to 8 nm, except for high Zr content films where a significant decrease in crystalline order is observed (grain size ~ 2.5 nm). In both series, the microstructure changed from equiaxed to columnar with increasing Al content. The highest hardness and strongest adhesion values were achieved in coatings with lower Zr and Al content. Conversely, the coatings with high Zr and the highest Al content exhibited an abrupt decrease in hardness, adhesion strength and toughness.     

Effect of Fe additions on microstructure and mechanical properties of a multi-component Nb–16Si–22Ti–2Hf–2Al–2Cr alloy at room and high temperatures

The phase constitutions, microstructural evolutions, and mechanical properties of Nb–16Si–22Ti–2Hf–2Al–2Cr–xFe alloys (where x = 1, 2, 4, 6 at.%, hereafter referred to as 1Fe, 2Fe, 4Fe and 6Fe alloys, respectively) prepared by arc-melting were investigated. It was observed that the nominal Fe content affected the solidification path of the multi-component alloy. The as-cast 1Fe alloy primarily consisted of a dendritic-like Nb_SS phase and (α+γ)-Nb₅Si₃ silicide, and the as-cast 2Fe and 4Fe alloys primarily consisted of an Nb_SS phase, (α+γ)-Nb₅Si₃ silicide and (Fe + Ti)-rich region. In addition to the Nb_SS phase, a multi-component Nb₄FeSi silicide was present in the as-cast 6Fe alloy. When heat-treated at 1350 °C for 100 h, the 1Fe and 6Fe alloys almost exhibited the same microstructures as the corresponding as-cast samples; for the 2Fe and 4Fe alloys, the (Fe + Ti)-rich region decomposed, and Nb₄FeSi silicide formed. The fracture toughness of the as-cast and heat-treated Nb–16Si–22Ti–2Hf–2Al–2Cr–xFe samples monolithically decreased with the nominal Fe contents. It is interesting that at room temperature, the strength of the heat-treated samples was improved by the Fe additions, whereas at 1250 °C and above, the strength decreased, suggesting the weakening role of the Nb₄FeSi silicide on the high-temperature strength. As the nominal Fe content increased from 1 at.% to 6 at.%, for example, the 0.2% yield strength increased from 1675 MPa to 1820 MPa at room temperature; also, the strength decreased from 183 MPa to 78 MPa at 1350 °C.     

Effect of swaging on microstructure and tensile properties of W–Ni–Fe alloys

The objective of this study was to investigate the effect of swaging on the microstructure and tensile properties of high density two phase alloys 90W–7Ni–3Fe and 93W–4.9Ni–2.1Fe. Samples were liquid phase sintered under hydrogen and argon at 1480 °C for 30 min and then 15% cold rotary swaged. Measurement of microstructural parameters in the sintered and swaged samples showed that swaging slightly increased tungsten grain size in the longitudinal direction and slightly decreased tungsten grain size in the transverse direction. Swaging increased the contiguity values in both longitudinal and transverse directions. Swaging led to more severe deformations at the edges than at the center of the specimens. Solidus and liquidus temperatures of the nickel-based binder phase in the sintered and swaged samples were determined by differential scanning calorimetry measurements. An increase in tensile strength with a reduction in ductility was observed due to strain hardening by swaging.     

Influence of Ce on microstructure and mechanical properties of LA141 alloys

LA141-（0-1.2）Ce alloys were prepared with vacuum induction melting method. The effects of Ce addition on the microstructure and mechanical properties of LA 141 alloys were studied. The microstructure and phases composition of these alloys were analyzed by optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffractometry. The mechanical properties of these alloys were measured with tensile tester. The results show that Ce has refining effect on the alloys. In the alloys, some Al2Ce compounds exist, which make the A1 content dissolved in a and β phases decrease and the hard brittle Mg17Al12 phase refined. The refining effect improves the mechanical properties of alloys. When Ce content is 0.9%（mass fraction）, the tensile strength reaches 206.8 MPa and the elongation is two times as high as that of LAl41 alloy. Due to the generation of Al2Ce, the content of Al solid soluted in β phase decreases resulting in the decrease of alloy hardness with the addition of Ce.