Effect of hot rolling on the enhancement of mechanical properties of low density Cu–Cr–Nb sintered alloy

Studies have been carried out on the effect of hot rolling on the enhancement of mechanical properties of sintered low density Cu–8 at.% Cr–4 at.% Nb alloy made from gas-atomised powders by vacuum hot pressing using varying pressure and temperature. The pressure is varied from 10 to 30 MPa whereas, 800, 900 and 1000 °C are three hot-pressed temperatures. Though hot rolling of porous low density hot-pressed samples results in near theoretical density, the hot-pressed sintered material with higher initial porosity shows lower strength and ductility after rolling. Hot-pressed compacts below certain density could not be rolled and the sample has cracked during rolling. The higher density material could be easily rolled and significant improvement in mechanical properties has been noticed. This has been attributed to the conversion of porosities into microscopic cracks which could not be healed due to the presence of Cr₂Nb precipitates. Finally, structure property correlation has been established.     

The effect of aging process on the microstructure and mechanical properties of a Cu–Be–Co–Ni alloy

The paper investigated the effect of two aging processes (i.e. normal aging and interrupted aging) on the microstructure and mechanical properties of a Cu–Be–Co–Ni alloy. The results of tensile and Kahn tear tests showed that the interrupted aging (IA) process could significantly improve the uniform elongation and plane stress fracture toughness with tiny decrease in ultimate tensile strength, when compared with the results from normal aging (NA) process. Under the scanning electron microscope, the fracture surface of samples treated by NA followed the intergranular fracture, while that of the samples treated by IA followed the transgranular fracture. The transmission electron microscope study revealed the differences between the microstructure of the alloy treated by NA and IA processes. After the NA process, the slender strip of γ′ precipitates aggregated at grain boundaries with a length of approximately 10 to 45 nm; the disk-shaped γ″ precipitates in the alloy treated by IA distributed homogenously throughout whole grains with a length of about 3 to 10 nm. The discussion of strengthening mechanisms demonstrated that the mechanism of precipitate shearing by dislocations made a contribution to the strengthening of the alloy treated by IA, while the Orowan mechanism was the dominant strengthening mechanism in the alloy treated by NA.     

Effect of cooling aging on microstructure and mechanical properties of an Al–Zn–Mg–Cu alloy

In the present work, Al–Zn–Mg–Cu alloy was aged by non-isothermal cooling aging treatment (CAT). At high initial aging temperature (IAT), the hardness was decreased with the decreased cooling rate. However, when IAT was lower than 180 °C, the hardness was increased with the decreased cooling rate. Conductivity was increased with the decreased cooling rate regardless of IAT. The tensile strength, yield strength and conductivity of Al alloy after (200–100 °C, 80 °C/h) CAT were increased 2.9%, 8.1% and 8.3% than that after T6 treatment, respectively. With an increase of IAT and decrease of cooling rate, the fine GP zone and η′ phase were transformed to be larger η′ and η precipitates. Moreover, continuous η phase at grain boundary was also grown to be individual large precipitates. Cooling aging time was decreased about 90% than that for T6 treatment, indicating cooling aging could improve the mechanical properties, corrosion resistance and production efficiency with less energy consumption.     

Effect of microstructure on the mechanical properties of as-cast Ti–Nb–Al–Cu–Ni alloys for biomedical application

The correlation between the microstructure and mechanical behavior during tensile loading of Ti_68.8Nb_13.6Al_6.5Cu₆Ni_5.1 and Ti_71.8Nb_14.1Al_6.7Cu₄Ni_3.4 alloys was investigated. The present alloys were prepared by the non-equilibrium processing applying relatively high cooling rates. The microstructure consists of a dendritic bcc β-Ti solid solution and fine intermetallic precipitates in the interdendritic region. The volume fraction of the intermetallic phases decreases significantly with slightly decreasing the Cu and Ni content. Consequently, the fracture mechanism in tension changes from cleavage to shear. This in turn strongly enhances the ductility of the alloy and as a result Ti_71.8Nb_14.1Al_6.7Cu₄Ni_3.4 demonstrates a significant tensile ductility of about 14% combined with the high yield strength of above 820 MPa already in the as-cast state. The results demonstrate that the control of precipitates can significantly enhance the ductility and yet maintaining the high strength and the low Young's modulus of these alloys. The achieved high bio performance (ratio of strength to Young's modulus) is comparable (or even superior) with that of the recently developed Ti-based biomedical alloys.     

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.     

Investigation on the mechanical properties and frictional performance of Ni–Cu–Si alloy

The microstructure evolution, mechanical properties and dry sliding behaviour of Ni–30Cu–xSi alloy have been investigated systematically. As the volume fraction of microscale second-phase particles and nanoscale precipitates increases, the hardness, yield strength and ultimate tensile strength of alloy are improved significantly but elongation is reduced. Through confocal laser scanning microscope and atomic force microscope, it is suggested that the wear mode changes from the mixture of abrasive and adhesive wear to single abrasive wear. Owing to the existence of netlike microscale second-phase particles which are more likely to split the matrix, the Ni–30Cu–5.5Si alloy exhibits an abnormal higher wear rate even with the highest hardness. The netlike structure which deteriorates the friction performance should be avoided in wear-resistant materials.     

Effect of CeLa addition on the mechanical properties of Al–Cu–Mn–Mg–Fe alloy

The rapid development of new energy automobiles leads to an increasing demand for high-strength lithium battery shell alloy. The microstructures, electrical conductivity and mechanical properties of CeLa-containing Al–Cu–Mn–Mg–Fe alloys were investigated with scanning electron microscopy (SEM), X-ray diffraction, Eddy Current conductivity tester, tensile testing and Erichsen cup testing. Experiment results indicate that Al₆(Mn, Fe) particles could be refined by CeLa alloying and AlCuCeLa phase nucleates and grew up at the surface of Al₆(Mn, Fe) particle. Major texture of the CeLa-containing alloys was different from that of the CeLa-free alloy. The electrical conductivity decreased with increase of the CeLa content. CeLa addition could greatly enhance the tensile strength of the alloy at temperatures ranging from –40°C to 300°C.     

Phase transformation during aging and resulting mechanical properties of two Ti–Nb–Ta–Zr alloys

Abstract

Phase transformations and mechanical properties of both Ti–29Nb–13Ta–4·6Zr and Ti–39Nb–13Ta–4·6Zr (wt–%) alloys were investigated. The microstructure of the 29Nb alloy is sensitive to solution and aging treatment. Ice water quenching from the solution treatment temperature resulted in (β+α") microstructure but air or furnace cooling led to a mixture of (β+ω). The formation of the orthorhombic α" martensite thus suppresses ω formation in the ice water quenched 29Nb alloy. Cooling rate from the solution treatment temperature also has a significant effect on the formation of α and ω phases during subsequent isothermal aging below the ω start temperature: slow cooling enhances ω but depresses α formation. This cooling rate dependence of aged microstructure was attributed to α" martensite acting as precursor of the α phase, thus providing a low energy path to the precipitation of a at the expense of ω. Phase transformation in the 39Nb alloy is more sluggish than that in the 29Nb alloy, owing to the presence of the higher content of β stabiliser Nb. For the 29Nb alloy, Young's modulus and mechanical properties are sensitive to the fraction of phases, and change significantly during aging, in contrast with the 39Nb alloy.     

Interfacial microstructures and mechanical properties of Sn–9Zn–0.5Ga–xNd on Cu substrate with aging treatment

The interfacial microstructures and mechanical properties of Sn–9Zn–0.5Ga–xNd on Cu substrate with aging treatment were investigated. Unlike the previous results, no Sn–RE phase was formed near the interface of Sn–9Zn–0.5Ga–xNd soldered joint after aging treatment at 150 °C for 1200 h. The combined action of Ga and Nd inhibited the formation of Sn–RE phase and resulted in an enhanced reliability of the soldered joint. The shear force of Sn–Zn–0.5Ga–0.08Nd soldered joint after aging treatment for 1200 h was twice the amount of Sn–9Zn joint and approaching the origin as-soldered joint of Sn–9Zn. Further, the fracture type of soldered joint still performed ductile after aging treatment for 1200 h. Synthesized the results of interfacial microstructures, mechanical test and fracture morphologies, Sn–9Zn–0.5Ga–0.08Nd solder has shown great potential to satisfy the increasing reliability requirements in electronics industry.     

Effects of solution treatment on the microstructure and mechanical properties of Al–Cu–Mg–Ag alloy

The effects of solution treatment on the microstructure and mechanical properties of Al–Cu–Mg–Ag alloy were studied by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), differential scanning calorimeter (DSC), transmission electron microscopy (TEM) and tensile test, respectively. The results show that the mechanical property increases and then decreases with increasing the solution temperature. And the residual phases are dissolved into the matrix gradually, the number fraction of the precipitation and the size of recrystallized grains increase. Compared to the solution temperature, the solution holding time has less effect on the microstructure and the mechanical properties of Al–Cu–Mg–Ag alloy. The overburnt temperature of Al–Cu–Mg–Ag alloy is 525 °C. The yield strength and the elongation get the best when the alloy is solution treated at 515 °C for 1.5 h, is 504 MPa and 12.2% respectively. The fracture mechanism of the samples is ductile fracture.     

Effect of grain refinement on the mechanical properties of Cu–Al–Be–B shape memory alloy

In this work, the mechanical properties of equal channel angular processing (ECAP)-processed fine- and coarse-grained Cu–11.42Al–0.35Be–0.18B shape memory alloys (wt.%) were evaluated using tensile testing. After eight passes of ECAP and subsequently quenching from 600 °C to RT, the mean grain diameter was refined from 227 μm to 42 μm with grain boundaries purified. The fine-grained alloy exhibited good mechanical properties with a high tensile strength (703 MPa) and featured deeper and closer dimples on its fracture surface. The micro cracks were more refined, and the cracks extension along the grain boundaries was improved in the fine-grained alloy. These changes can be attributed to improvement of martensite morphology, structural refinement and grain boundary purification.     

Effects of environmental aging on the mechanical properties of bamboo–glass fiber reinforced polymer matrix hybrid composites

Short bamboo fiber reinforced polypropylene composites (BFRP) and short bamboo–glass fiber reinforced polypropylene hybrid composites (BGRP) were fabricated using a compression molding method. Maleic anhydride polypropylene (MAPP) was used as a compatibilizer to improve the adhesion between the reinforcements and the matrix material. By incorporating up to 20% (by mass) glass fiber, the tensile and flexural modulus of BGRP were increased by 12.5 and 10%, respectively; and the tensile and flexural strength were increased by 7 and 25%, respectively, compared to those of BFRP. Sorption behavior and effects of environmental aging on tensile properties of both BFRP and BGRP systems were studied by immersing samples in water for up to 1200 h at 25°C. Compared to BFRP, a 4% drop in saturated moisture level is seen in BGRP. After aging in water for 1200 h, reduction in tensile strength and modulus for BGRP is nearly two times less than that of BFRP. Use of MAPP as coupling agent in the polypropylene matrix results in decreased saturated moisture absorption level and enhanced mechanical properties for both BFRP and BGRP systems. Thus it is shown that the durability of bamboo fiber reinforced polypropylene can be enhanced by hybridization with small amount of glass fibers.     

Effects of stress-aging on the microstructure and properties of an aging forming Al–Cu–Mg–Ag alloy

The effects of stress-aging on the microstructure and properties of Al–Cu–Mg–Ag alloy were studied by hardness test, electric resistivity test, optical microscopy and transmission electron microscopy. The results show that the application of external stress during aging did not change the grain morphology of Al–Cu–Mg–Ag alloy, but resulted in great changes of the precipitations. The precipitation of θ^′ phases was promoted while that of Ω phases was restrained and the initial hardening rate of the alloy decreased. This might originate from the large amounts of dislocations during stress-aging that provided sites facilitating heterogeneous nucleation of θ^′ phases. This was verified by the phenomenon that the density of θ^′ phases increased while that of Ω phases decreased and the peak hardness was reduced when Al–Cu–Mg–Ag alloy was cold deformed with 6% stretch prior to aging.     

Non-isothermal aging of a high-Zn-containing Al–Zn–Mg–Cu alloy: microstructure and mechanical properties

The non-isothermal aging behaviour of a newly developed Al–Zn–Mg–Cu alloy containing 17?wt-% Zn was investigated. Hardness and shear punch tests demonstrated that during non-isothermal aging, the mechanical properties of the alloy first increased and then decreased. The best properties were obtained in a sample which was non-isothermally aged upto 250°C with heating rate of 20°C?min^?1, due to the presence of η′/η (MgZn₂) phases. This was confirmed by differential scanning calorimetery. After homogenisation, residual eutectic phases remained at triple junctions or in a spherical form. During aging, these phases transformed into rodlike S (Al₂CuMg)-phase at 400°C, with sizes ranging from 50 to 250?nm. The precipitation sequence in this high-Zn alloy was similar to that for conventional Al–Zn–Mg–Cu alloys.     

Review: effect of bimetal interface structure on the mechanical behavior of Cu–Nb fcc–bcc nanolayered composites

This article reviews the growing body of work over the past decade investigating the effect of interface crystallographic character and resulting local interface structure on the mechanical behavior in bimetallic nanolayered composites. It has been shown that nanolayered composites exhibit enhanced strength, thermal stability, radiation damage tolerance, and resistance to shock deformation in comparison to their coarse-grained constituents. These unique behaviors are attributable to the high density of interfacial content, as well as the local interface structure and its influence on mechanically or irradiation-induced defects. Here, we cover recent literature on Cu–Nb nanolayered composites synthesized via different pathways including physical vapor deposition and severe plastic deformation techniques such as accumulative roll bonding. By altering the synthesis method, we can produce materials with similar chemical composition and layered morphology, while varying only the crystallographic character of the interface as defined by the orientation relationship and interface plane. This capability, in turn, opens an unprecedented opportunity for systematic investigation of the local interface structure on subsequent behavior, while keeping all other variables constant. We begin with a discussion of interface structures that develop as a function of their processing path. We then follow with the effects of interface structure on dislocation nucleation and deformation twinning. Next, we discuss interface effects on mechanical behavior at quasi-static ambient conditions and later under extreme strains, strain rates, and temperatures. Taken together, these examples provide a strong indication that interface structure matters. The exciting implication is that bimetal interfaces can potentially be engineered for optimal material performance.     

Effects of Nb content in Ti–Ni–Nb brazing alloys on the microstructure and mechanical properties of Ti–22Al–25Nb alloy brazed joints

Vacuum brazing was successfully used to join Ti–22Al–25Nb alloy using Ti–Ni–Nb brazing alloys prepared by arc-melting. The influence of Nb content in the Ti–Ni–Nb brazing alloys on the interfacial microstructure and mechanical properties of the brazed joints was investigated. The results showed that the interfacial microstructure of brazed joint consisted of B2, O, ?3, and Ti2 Ni phase, while the width of brazing seams varied at different Nb contents. The room temperature shear strength reached359 MPa when the joints were brazed with eutectic Ti40Ni40Nb20 alloy at 1180?C for 20 min, and it was321, 308 and 256 MPa at 500, 650 and 800?C, respectively. Cracks primarily initiated and propagated in ?3compounds, and partially traversed B2+O region. Moreover, the fracture surface displayed typical ductile dimples when cracks propagated through B2+O region, which was favorable for the mechanical properties of the brazed joint.     

Effect of heat treatment on microstructure and mechanical properties of Cr–Ni–Mo–Nb steel

Abstract

The microstructure and mechanical properties of a medium carbon Cr–Ni–Mo–Nb steel in quenched and tempered conditions were investigated using transmission electron microscopy (TEM), X-ray analysis, and tensile and impact tests. Results showed that increasing austenitisation temperature gave rise to an increase in the tensile strength due to more complete dissolution of primary carbides during austenitisation at high temperatures. The austenite grains were fine when the austenitisation temperature was <1373 K owing to the pinning effect of undissolved Nb(C,N) particles. A tensile strength of 1600 MPa was kept at tempering temperatures up to 848 K, while the peak impact toughness was attained at 913 K tempering, as a result of the replacement of coarse Fe rich M₃C carbides by fine Mo rich M₂C carbides. Austenitisation at 1323 K followed by 913 K tempering could result in a combination of high strength and good toughness for the Cr–Ni–Mo–Nb steel.     

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.     

Influence of second phases on mechanical properties of spray-deposited Al–Zn–Mg–Cu alloy

Al–10.66Zn–2.48Mg–1.41Cu–0.17Zr–0.17Sc (wt.%) alloy prepared by spray deposition was processed with different hot deformation followed by heat treatment. The mechanical properties and microstructure evolution were investigated. The results indicate that uniform ultimate tensile strength of 774 MPa, yield strength of 734 MPa and elongation of 13.7% are obtained with two-step hot deformation, which increase by 2.7%, 3.82% and 95% compared with one-step hot deformation. Microstructural observations show that increase of elongation is mainly ascribed to high volume fraction of smaller precipitates and reduction of stress concentration areas as a result of disappearance of the coarse second phases. The fractured tensile specimens with two-step hot deformation exhibit dimple fractographic features. Improvement of strength is attributed to the precipitation strengthening and dispersed strengthening.