反挤压Zn-Mn二元合金的微观组织与力学性能

采用电子背散射衍射(EBSD)和室温拉伸试验,研究了不同挤压速度对Zn-Mn二元合金的微观组织与力学性能的影响.研究结果表明,挤压态Zn-Mn二元合金发生完全动态再结晶.在相同的Mn质量分数下,随着挤压速度的提高,Zn-Mn二元合金的强度上升、塑性下降,平均晶粒尺寸增加.晶粒尺寸和第二相是影响Zn-0.3Mn和Zn-0.7Mn力学性能的主要因素.在相同的挤压速度下,随着Mn质量分数的增加,第二相尺寸和数量增加,平均晶粒尺寸减小,但Zn-Mn二元合金的强度下降,伸长率显著上升.     

Microstructural evolution and mechanical properties of a forged gamma titanium aluminide alloy

A two-phase gamma titanium aluminide alloy, Ti-47Al-1Cr-1V-2.5Nb (in at.%), was studied under forged and various subsequent heat treatment conditions, to investigate the microstructural evolution and the effect of microstructure on room temperature (RT) tensile properties and fracture toughness behavior. Four classes of microstructure and three types of lamellar formation were identified, and their formation mechanisms were analyzed using various analytical techniques including metallography, electron optics, differential thermal analysis (DTA), and crystallography. It was found that both tensile and toughness behavior were profoundly affected by the microstructural variations.     

Microstructural evolution and mechanical properties of AlCrFeNiCoC high entropy alloy produced via spark plasma sintering

AlCrFeCoC high entropy alloy was synthesised through mechanical alloying and spark plasma sintering. The milling time had a strong influence on the particles shape and structure and consequently on microstructural and mechanical evolution of the material after sintering. The material's microstructure after spark plasma sintering contained FCC and BCC phases as well as ordered BCC and C₂₃C₆ carbide. The material's strength increased with increasing the milling time because of the finer microstructure and phases formation evolution.     

Microstructural evolution and mechanical properties of the AA8011 alloy during the accumulative roll-bonding process

The investigation of the microstructure and mechanical properties has been conducted on an AA8011 alloy produced by a novel intense plastic straining process named accumulative roll bonding. The results show that an ultrafine-grained 8011 alloy, having a mean grain (or subgrain) size less than 1 μm, was successfully accumulative roll-bonded (ARB) at room temperature (RT-ARB) and at 200 °C (HT-ARB). The average grain (or subgrain) sizes of the RT-ARB and HT-ARB samples were reduced greatly from about 25.8 μm initially to 650 to 700 nm and 800 to 900 nm, respectively. After several cycles of accumulative roll bonding, most regions of this material were filled with ultrafine grains with high-angle boundaries. The ambient tensile strengths of the RT-ARB and HT-ARB samples increased with equivalent strain only up to the strain of 2.4. After that, the strengths of the RT-ARB samples nearly leveled off, and the strengths of the HT-ARB samples decreased with equivalent strain above the strain of 2.4. Furthermore, the elongation in both the RT-ARB and HT-ARB samples decreased greatly after the first cycle and then increased continuously with strain. The softening behavior happened in HT-ARB samples above a strain of 2.4, which is mainly attributed to the continuous recrystallization, dynamic recovery, and static recovery during and/or after the accumulative roll-bonding process.     

Microstructural evolution and mechanical properties of Cr-Ru alloys

In an effort to enhance ductility and strength of Cr-base alloys, a series of Cr-Ru alloys with Ru contents ranging from 3 to 30 at. pct were made to study their microstructure evolution and mechanical properties. The microstructure of the alloys with 6 to 20 at. pct Ru showed signs of a eutectic structure. However, no corresponding eutectic reaction is indicated in the published Cr-Ru phase diagram. The yield strength of the Cr-Ru alloys increased with increasing Ru content at both room temperature and 1200 °C. The tensile ductility of Cr-3 at. pct Ru is about 1.5 pct at room temperature, while the alloys containing 6 at. pct or more Ru showed zero tensile elongation. The deformation mechanisms of the Cr-Ru alloys are discussed in terms of the microstructure and fracture behavior. This article is based on a presentation made in the symposium entitled “Beyond Nickel-Base Superalloys,” which took place March 14–18, 2004, at the TMS Spring meeting in Charlotte, NC, under the auspices of the SMD-Corrosion and Environmental Effects Committee, the SMD-High Temperature Alloys Committee, the SMD-Mechanical Behavior of Materials Committee, and the SMD-Refractory Metals Committee.     

钼-铼-镧合金微观组织及力学性能研究

通过固-液掺杂法在Mo-Re合金中加入稀土La₂O₃纳米颗粒制备得到Mo-Re-La合金, 将Mo-Re-La合金与Mo-Re合金、纯Mo的微观组织及力学性能进行对比研究, 得到如下结论: 在纯Mo中添加低含量Re元素(质量分数3.5%) 对Mo-Re合金有明显的细晶强化效果; 将La₂O₃纳米颗粒加入Mo-Re合金进一步细化和强化了Mo-Re-La合金。     

Microstructural development of a gas-atomized and hot-pressed super-α2 alloy

A variety of heat treatments have been employed to explore the microstructure in Ti-25Al-10Nb-3V-lMo alloy prepared by gas atomization and hot pressing. These treatments include quenching by oil cooling and water cooling and aging at temperatures between 530 °C and 950 °C. Quenching transformations from the β-phase field include the formation ofO phase in oil quenching and β (disordered) +O phase in water quenching. The metastable β phase decomposes intoO + “Ω”,O, or α₂ + β_o/B2 phase when the as-quenched alloy is aged at various temperatures. By comparing the selection area diffraction patterns, it has been found that the ordered w phase in the alloy studied in this article is distinct in structure to the “Ω type” (P3m1) and B8₂ phase which are formed in the parent matrix of the ordered β(B2,D0₃) phases. It has also been shown by X-ray diffraction (XRD) analyses that the lattice parameters of the as-agedO phase do not remain constant in the alloy at various temperatures.     

Ultrafine-grained microstructures and mechanical properties of alloy steels

Ultrafine-grained microstructures can be developed in a variety of alloy steels by coldworking followed by annealing in theα +γ region. Because the annealing temperatures are relatively low and the recrystallized structure is two-phase, grain growth is restricted. Specimens with grain sizes in the range 0.3 to 1.1 μ.m (ASTM 20 to 16) were obtained in manganese and nickel steels by annealing 1 to 400 hr at temperatures between 450° and 650°C (840° to 1200°F). The expected improvement in yield strength through grain refinement was observed in almost all alloys. Other tensile properties depend on factors such as grain size, austenite stability, and specimen geometry, that determine which of three types of plastic behavior will occur. Transformation of austenite during straining improves the mechanical properties of ultrafine-grained specimens.     

Internal oxidation and mechanical properties of TZM-Mo alloy

The internal oxidation behavior of the bcc alloy TZM-Mo (Mo-0.5 wt pct Ti-0.08 wt pct Zr-0.02 wt pet C) was investigated in low-pressure O₂, CO, and H₂O environments at 1098 and 1273 K. The results indicate that a diffusion process controls the kinetics of the oxygen absorption at 1098 K, while bulk diffusion and gas-metal interaction at the specimen surface both affect the rate at 1273 K. The carbon content of TZM in these experiments increased initially and then decreased. Decarburization became significant only after extended exposure at 1273 K. The deformation and fracture behavior of both oxidized and heat-treated TZM specimens were studied at temperatures to 1589 K. TZM specimens showed an increase in strength and a linear decrease in ductility with oxygen content. Oxidized TZM lost its ductility completely at an oxygen level of 300 ppm at room temperature, 1366, and 1589 K, but 500 ppm was required at 1098 K. The ductility of embrittled TZM was increased significantly with heat treatment at high temperatures and was almost completely restored after annealing at 1973 K. The change in mechanical properties is discussed in terms of internal oxidation and precipitation of oxides.     

Fe-Cu-Sn烧结体的显微组织与力学性能

分别采用水雾化Fe-30%Cu合金粉末和单质Sn、Fe、Cu元素粉末为原料制备Fe-Cu-Sn合金,研究原料粉末和Sn含量(质量分数)对Fe-Cu-Sn烧结体致密度、冲击韧性、硬度和抗弯强度的影响。结果表明:与采用元素混合粉末相比,采用合金化程度较高的Fe-30%Cu(质量分数,下同)合金粉末为原料能大幅提高850℃烧结的Fe-Cu-5%Sn合金的致密度和力学性能,其致密度由82.8%提高到94.3%,硬度、冲击韧性和抗弯强度分别提高52%、84%和109%;当Sn的质量分数w(Sn)为3%～15%时,随着Sn质量分数增加,合金的硬度增大,冲击韧性和抗弯强度先增加后减小,其中w(Sn)为5%时,其抗弯强度和冲击韧性都较高,分别为977 MPa和11.6 J/cm2。当烧结体为双重结构组织时,其力学性能显著提高。     

On the precipitation-hardening behavior of the Al-Mg-Si-Cu alloy AA6111

The precipitation-hardening behavior of aluminum alloy AA6111 during artificial aging and the influence of prior natural aging on the aging behavior were investigated. The evolution of microstructure was studied using quantitative transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The evolution of the relative volume fraction of precipitates for the solution-treated alloy was determined using isothermal calorimetry and a new analysis based on the DSC technique. Quantitative TEM was also used to obtain the rate of precipitation of microscopically resolvable phases during aging at 180 °C. Three types of precipitates, i.e., unresolved Guinier-Preston (GP) zones, β″, and Q′, were found to form during aging at 180 °C. The evolution of yield strength was related to the evolution of microstructure. It was found that the high hardening rate during artificial aging for the solution-treated alloy is due to the rapid precipitation of the β″ phase. Natural aging prior to artificial aging was found to decrease the rate of precipitation of β″. The slow hardening rate for the naturally aged alloy was attributed to the slower nucleation and growth of β″ phase.     

The sequence of precipitation in the Al-Mg-Si-Cu alloy AA6111

The preciptation behavior of the aluminum alloy AA6111 in the advanced stages of aging has been studied using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM). The results have demonstrated the formation of various precipitate types and morphologies of quaternaryQ phase andβ (Mg₂Si) families at the peak-aged condition and during overaging at different temperatures. The work has clarified the sequence ofQ phase formation and showed evidence for a new morphology of this phase. The sequence of precipitation in AA6111 is elaborated in light of the new findings.     

Microstructural and mechanical properties investigation of electrodeposited and annealed LIGA nickel structures

Lithographic, Galvanoformung, Abformung (LIGA) component fabrication is a process in which structural material is deposited into a patterned polymethyl-methacrylate (PMMA) mold realized through deep X-ray lithography. The process permits fabrication of metal microelectrome chanical systems (MEMS) components with representative dimensions that range from a few microns to several millimeters. This investigation characterizes the microstructure and mechanical properties of LIGA-fabricated nickel (LIGA Ni), electrodeposited using Watts bath and sulfamate bath chemistries. As a prelude to studying high-temperature joining processes in LIGA Ni components, an annealing investigation was conducted on samples fabricated from both bath chemistries. Mechanical properties and microstructural analyses on as-deposited and annealed samples were conducted using a mini servohydraulic load frame and the electron backscatter diffraction (EBSD) microtexture measurement technique. The deposits were found to have fine-grain, highly textured microstructures oriented with an acicular or columnar morphology relative to the plating direction. Previously uncharacterized, anomalous, local spatial variations in the crystallographic texture of the as-deposited microstructures were identified by EBSD analyses. Microstructural evolution during annealing seemed to follow a recovery, recrystallization, rapid grain-growth microstructural-evolution mechanism in LIGA Ni deposited from the Sulfamate bath chemistry and simply a recovery and grain-growth microstructural-evolution mechanism in LIGA Ni deposited from the Watts bath chemistry. The evolution of microstructure in the annealed samples corresponded with a dramatic drop in their strength and determined the limiting diffusion-bonding temperature for LIGA Ni components.     

Microstructural evolution and mechanical properties of laser-welded joints of medium manganese steel

The cold-rolled 5% medium Mn steel was butt-welded using a fiber laser.The microstructure,distribution of microhardness,and tensile properties of the base metal(BM)and welded joint were investigated.The results showed that the fusion zone of the welded joint had the highest microhardness due to the formatio n of 100%marten site.A finely mixed microstructure of martensite,ferrite,and austenite was formed in the heat-affected zone,and there was no softened zone in this area.The tensile test results indicated that the ultimate tensile sirength and yield strength were higher for the joint than for BM.The joint efficiency was approximately 100%.All samples of the welded joirn failed at the location of BM during tensile deformation.The fracture surfaces of the BM and welded joint were mainly ductile fractures.The BM and welded joint exhibited strain rate independence of the tensile strength and yield strength at strain rates of 0.01-1 s_1,while the yield strength of the BM and welded joint increased rapidly when the strain rate reached 5 s_1 due to changes in the dislocation moveme nt mechanisms.The uniform elongation of the BM and welded joint decreased with in creasing strain rate.     

Microstructural modelling of electrical conductivity and mechanical properties of sintered ferrous materials

Abstract

The role of microstructure on mechanical properties of sintered ferrous materials was studied using a method based on electrical conductivity measurement. The method was accompanied by quantitative fractography to evaluate the dewaxing and sintering process in iron compacts. The effects of manufacturing parameters, such as compacting pressure in the range of 150–800 MPa, sintering temperature from 400 to 1300°C, sintering time up to 8 h, and lubrication mode were investigated. Several mathematical models were checked to obtain the best one for prediction of electrical conductivity changes as a function of manufacturing parameters. The mechanical properties of the sintered compacts were also evaluated to establish a relationship between conductivity, total porosity, pore morphology, and mechanical behaviour. The results show that the electrical conductivity/resistivity of sintered materials is closely related to its microstructure, so that measuring these properties can replace destructive test methods for prediction of mechanical strength of sintered materials with homogeneous matrix microstructure. The application of the method is shown for sintered Fe, Fe–0·8%C, and Fe–1·5%Mo–0·7%C compacts.     

Microstructural refinement and mechanical properties improvement of elemental powder metallurgy processed Ti-46.6Al-1.4Mn-2Mo alloy by carbon addition

Strengthening of a gamma TiAl alloy was sought by a chemical modification of the composition with carbon. Up to 0.6 at. pct of carbon was added to the Ti-46.6Al-1.4Mn-2Mo alloy processed by elemental powder metallurgy. Carbon addition resulted in considerable microstructural changes such as refinement, by a factor of about 2, of the lamellar microstructure and carbide precipitation. The cause of the lamellar structure refinement is twofold, increased heterogeneous nucleation rate and decreased γ platelet growth rate, the net result of which was a retarded diffusional transformation kinetics of α to α/γ lamellae. As a consequence of the microstructural changes, the high-temperature tensile properties and the creep properties of the alloy were significantly improved. Anomalous hardening was also observed at 800 °C, resulting in a tensile yield strength of 700 MPa. The strengthening effect of carbon was realized by the microstructural refinement and by precipitation hardening of intergranular as well as interlamellar Ti₃AlC. In terms of the tensile properties and the creep properties, the optimum amount of carbon addition was 0.3 at. pct.     

Microstructural damage and residual mechanical properties in helium-bearing gas metal Arc weldments

The influence of entrapped helium on microstructural damage and residual mechanical properties subsequent to applying low-penetration gas metal arc (GMA) weld overlays was examined for an AISI Type 304 stainless steel. Two helium levels were examined: 22.5 and 85.0 atomic parts per million (appm) He. Detailed scanning electron microscopy (SEM) revealed the presence of intergranular cracks in the weld heat-affected zone (HAZ). The crack surfaces exhibited a dimple structure that was characteristic of a gas bubble embrittled material. Transmission electron microscopy (TEM) revealed that the size and spacing of the grain boundary helium gas bubbles remained virtually unchanged (relative to that established by the charging and aging procedure) at distances greater than 1 mm from the fusion line. Within this first millimeter, the diameter of the bubbles increased rapidly, and the bubble spacing increased to the characteristic spacing of the dimples that decorated weld-induced cracks. Mechanical testing revealed a loss in strain-to-fracture and ultimate tensile strength (UTS) at the higher helium level. While the majority of the fracture occurred in a transgranular, ductile manner, some deformation-induced intergranular cracking was observed. This cracking occurred over a very narrow region localized to the HAZ of the weldment. At the lower helium level, ductility and strength were unaffected compared to helium-free specimens.     

Al-Mg-Si-Cu合金近液相线半连续铸造组织研究

采用近液相线半连续铸造方法制备了Al-1.2Mg-0.8Si-0.4Cu合金半同态锭坯,研究了浇注温度和铸造速度对锭坯微观组织的影响.合金熔体在750℃下浇注,组织不均匀,边部是细小的晶粒,1/2半径和中心部位是粗大的枝晶,最小晶粒直径25 μm,最大晶粒直径达220μm;660℃保温后浇注,可以获得适合半固态加工的均匀、细小的近球形组织,锭坯中心和边部组织差异小,平均品粒尺寸为36.5μm;铸造速度达150 mmm/min时有利于均匀、细小的近球形组织形成.结果表明,对于Al-1.2Mg-0.8Si-0.4Cu铝合金采用近液相线半连续铸造可以获得理想的半固态浆料.     

Tempaloy AA-1钢时效组织结构及力学性能分析

 通过进行650 ℃高温时效试验,研究了Tempaloy AA-1钢在时效过程中M23C6合金相的析出与室温力学性能和冲击韧性的关系,并利用扫描电镜和透射电镜对材料在不同时间时效后Tempaloy AA-1的组织结构和室温冲击断口进行观察。结果表明：随着Tempaloy AA-1钢时效时间的增加,逐渐析出M23C6合金相,并稳定地分布在晶界处。Tempaloy AA-1时效500 h后,由于晶界处M23C6碳化物强化作用,屈服强度与抗拉强度达到最大值;时效8 000 h后,晶界处M23C6碳化物颗粒聚集增大,晶界强化作用弱化, Tempaloy AA-1钢的强度略有降低。长期时效后M23C6 型碳化物没有发现其过度团聚,因此,Tempaloy AA-1钢仍具有良好的时效冲击韧性。Tempaloy AA-1时效后具有良好的力学性能和冲击韧性是由于材料在长期高温时效后具有良好的组织稳定性。     

低氧MHC合金板材的制备及力学性能

采用粉末冶金方法和热轧工艺制备了低氧MHC合金轧制板材,通过化学分析、金相分析、硬度测试、拉伸力学性能测试研究了低氧MHC合金的显微组织和力学性能。研究表明：通过调节C/Hf原子比、钼粉还原并结合真空烧结等手段,可以有效降低合金中的氧含量。不同温度下退火后样品显微组织分析和力学性能测试结果对比表明,合金板材在1 300℃以下为回复阶段,随着退火温度的增加,1 300℃开始发生再结晶,强度和硬度逐渐下降,塑性提高,在1 600℃时再结晶完成,完全再结晶的低氧MHC合金板材塑性优异。