一种适用于通讯器材的铝锰合金开发研究

测试了不同锰含量Al—Mn合金的硬度和冲击韧性,分析了锰含量对Al—Mn合金断口形貌特征及断裂形式的影响。结果表明：随着锰含量的增加Al—Mn化合物数量增加,Al—Mn合金铸态硬度提高,冲击韧性降低;随着锰含量的增加Al—Mn化合物形态由细变粗,由长变短,由头部圆形转变具有尖角形块状,材料的冲击韧性急剧下降。随着锰含量的增加Al—Mn合金断口形貌由塑性断裂向准解理断裂、脆性断裂特征变化。     

Al和Mo含量对热等静压制备的FeCrAlMo合金组织及拉伸性能的影响

FeCrAl合金由于具有良好的高温抗氧化性能和力学性能而广泛应用于高温和氧化性气氛环境。本研究通过粉末热等静压制备出Fe-22Cr-3Al-3Mo和Fe-22Cr-2Al-5Mo两种成分的合金,对粉末的显微组织、热等静压后两种成分合金的组织及拉伸性能进行对比分析,结果表明:Fe-22Cr-3Al-3Mo合金20℃时的强度和塑性都高于Fe-22Cr-2Al-5Mo合金,而500℃时的强度和塑性都低于Fe-22Cr-2Al-5Mo合金;Fe-22Cr-3Al-3Mo合金中析出相主要为分布在晶界及晶内的细小AlN相及少量粗大的富Cr相,Fe-22Cr-2Al-5Mo合金中析出相主要为大尺寸的富Cr碳氧化物;Al含量降低、Mo含量增加,晶界形成较多的大尺寸富Cr相,导致Fe-22Cr-2Al-5Mo合金在20℃时塑性较差。     

TC18钛合金的组织和性能与热处理制度的关系

通过三因素三水平正交设计方法研究了两阶段退火热处理制度的三个温度阶段对TC18钛合金性能、组织的影响,定量分析了合金热处理温度变化对总体性能的影响,结果表明,在本文试验条件下可通过提高中温温度、降低低温温度来提高合金的强度,降低高温温度、提高低温温度可改善合金的塑性,通过降低高温温度或中温温度可提高合金的冲击韧性,显微组织分析表明,TC18钛合金的强度主要受未转变β组织及在其上产生的次生αs相的总的含量、次生αs相的含量、形状的控制;合金的塑性受初生αp相形状及次生αs相的数量、形状控制;合金的冲击韧性受初生αp相的含量及形状控制.     

Al对GH4169合金冲击性能的影响

研究了Al对GH4169合金晶界相的析出和冲击性能的影响.结果表明,提高Al含量可抑制晶界δ相的析出,促进晶界Laves相、M7C3相和σ相等有害相的析出;随着Al含量的提高,GH4169合金的室温冲击性能明显降低,冲击断口由穿晶型转变为沿晶型.提高Al含量所导致的Laves相等有害脆性相的析出降低了晶界强度,使晶界裂纹更容易萌生和扩展,降低了GH4169合金的冲击韧性.     

机械合金化方法制备AlxCoCrCu0.5FeNi高熵合金组织结构和性能研究

采用机械合金化和真空热压烧结方法制备了Al_xCoCrCu_(0.5)FeNi高熵合金,研究Al含量对合金系的晶体结构、显微组织、硬度、压缩性能以及摩擦磨损行为的影响。球磨60h和真空热压烧结后的晶体结构均为FCC和BCC双相结构,但相对含量发生变化。Al含量的增加使合金塑性降低,硬度和强度增大,低Al含量的Al_0、Al_(0.5)合金塑性好,强度低,压缩量高达30%和25.6%;高Al含量的Al_(1.0)、Al_(1.5)合金塑性较差,强度高,压缩强度达到1855MPa和2083 MPa,原子半径大的Al含量增加造成严重的晶格畸变,使固溶强化效应增加是合金硬度和强度升高的主要原因。随着Al含量的增加,合金的断裂方式由韧性断裂向脆性断裂转变。合金的耐磨性与硬度呈正相关关系,Al_0、Al_(0.5)、Al_(1.0)的磨损机制为黏着磨损与磨粒磨损,Al_(1.5)合金则为磨粒磨损。     

SPS烧结参数对Ti3Al2Mo5Nb室温及低温力学性能的影响

目的 研究SPS烧结温度、保温时间等工艺参数对Ti3Al2Mo5Nb在不同温度下力学性能的影响规律.方法 利用放电等离子烧结(SPS)技术快速烧结,得到致密度较高的Ti3Al2Mo5Nb低温钛合金,通过设置不同的烧结温度及保温时间,结合室温及77 K低温力学性能测试,对不同参数得到的合金的室温及低温性能进行表征,探究SPS烧结过程中工艺参数对Ti3Al2Mo5Nb合金室温及低温力学性能的影响规律.结果 随着烧结温度的升高,合金的致密度、硬度逐渐提高,室温条件下的抗拉强度逐渐提高,伸长率逐渐降低,而77 K条件下合金的抗拉强度逐渐增加,伸长率先增加后减少.随着保温时间的增加,合金的致密度及硬度变化不大,无论在室温还是在77 K低温条件下,合金的强度均先减小后增加,伸长率逐渐减少.微观组织显示,随着烧结温度的增加,β相含量逐渐减少,与伸长率的变化相同,这可能是由于β相的存在促进了室温变形过程中晶界滑移及低温条件下产生孪晶;随着保温时间的增加,析出的强化相含量先减少后增加,这可能是导致合金强度变化的原因,同时β相含量减少,从而导致合金在273 K及77 K条件下的塑性均降低.结论 对低温条件下使用的钛合金而言,在50 MPa压力下,当温度为1050℃时,保温5 min得到的样品力学性能最好,过高的烧结温度及保温时间会减少合金中β相含量,降低低温塑性.     

Ti3SiC2陶瓷颗粒增强铜基复合材料的组织和性能

为了考察Al,Sn,Zr,Mo合金元素对α钛合金在室温和77 K低温(液氮)下的缺口冲击韧性(冲击值Ak)的影响,采用示波冲击试验机测试了Ti-2Al,Ti-2Sn,Ti-2Zr和Ti-1Mo 4种α钛合金在室温和77K下的Ak值,并计算了表征其冲击韧性的弹性变形功、塑性变形功和裂纹扩展撕裂功.用扫描电镜观察了4种合金冲击试样断口的形貌.计算数据和显微组织表明,4种合金均显示韧性特征,4种合金元素对冲击韧性贡献的顺序为:Mo＞Zr＞Sn＞Al.     

α钛合金在室温和低温的冲击韧性

为了考察Al,Sn,Zr,Mo合金元素对α钛合金在室温和77 K低温(液氮)下的缺口冲击韧性(冲击值Ak)的影响,采用示波冲击试验机测试了Ti-2Al,Ti-2Sn,Ti-2Zr和Ti-1Mo 4种α钛合金在室温和77K下的Ak值,并计算了表征其冲击韧性的弹性变形功、塑性变形功和裂纹扩展撕裂功.用扫描电镜观察了4种合金冲击试样断口的形貌.计算数据和显微组织表明,4种合金均显示韧性特征,4种合金元素对冲击韧性贡献的顺序为:Mo＞Zr＞Sn＞Al.     

锰元素对TWIP钢层错能和变形机制的影响

根据层错能的热力学模型,计算了Fe-XMn-3Si-3Al 系高强度高塑性TWIP钢的层错能.计算结果表明,随锰含量增加Fe-XMn-3Si-3Al系 TWIP钢层错能增加,在此基础上讨论了锰含量对Fe-XMn-3Si-3Al 系TWIP钢变形机制、力学性能和微观组织的影响.在合金中Mn含量的提高使层错能增加,而层错能的增加使Fe-XMn-3Si-3Al系钢表现出不同的变形机制,即逐渐由TRIP效应变为TWIP效应;同时随着Mn含量的提高,合金的抗拉强度降低,而塑性提高.     

微量B元素对铸造Ti2AlNb合金组织与力学性能的影响

目的 研究微量B元素对铸造Ti2AlNb合金组织和力学性能的影响,优选出适合铸造工艺的Ti2AlNb合金成分,为推进铸造Ti2AlNb合金的应用提供理论和数据支撑。方法 以Ti–22Al–25Nb(原子数分数,下同)、Ti–22Al–24Nb–0.1B、Ti–22Al–24Nb–0.2B合金为研究对象,采用光学显微镜、扫描电镜研究不同B含量合金铸态、热等静压态的宏、微观组织及析出相形态。采用XRD分析合金的物相组成,室温拉伸性能测试评价力学性能,通过扫描电镜观察拉伸断口,分析微量B元素对力学性能产生影响的原因。结果 添加微量B元素可以明显细化Ti–22Al–25Nb合金的晶粒尺寸,随着B元素原子数分数增加至0.2%,晶粒尺寸由958 μm减小至548 μm。B元素在合金中主要以固溶态、TiB和TiB2针片状析出相形式存在,随着B含量的增加,硼化物长度和厚度尺寸略微增加、体积分数由0.3%增加至0.8%。0.1B合金的室温屈服强度、抗拉强度和伸长率与原合金水平相当,0.2B合金的屈服强度提升,但其抗拉强度和伸长率均降低。断口分析显示,0.2B合金塑性降低是硼化物增多、集中分布引起脆性断裂所致。结论 综合B元素对流动性的改善效果,优选出适合铸造工艺的合金成分为Ti–22Al–24Nb–0.1B。     

The influence of manganese addition on mechanical properties of commercial Al‐4Mg casting alloys

The aim of this study was to investigate the mechanical properties of Al‐Mg‐Si alloys aged to peak hardness with different dispersoid volume fraction. It was found that the tensile strength increases with dispersoid content, for alloys having similar ductility. The effect of an increasingly triaxial stress state on a fracture strain above mentioned alloys were measured using a series of notched tensile specimens whose notch root radius of curvature was changed. The alloy ductility was found to increase with dispersoid content and root radius and to decrease with increased stress triaxiality. The fracture toughness of these alloys was determined as a function of dispersoid content and notch root radius of curvature. It was observed that the fracture toughness increased as the dispersoid content and the notch root radius increased. scanning electron microscope analysis of the fracture surfaces revealed that fracture mechanism was transgranular fracture with dimples formation. It is argued that optimum mechanical properties in these alloys can be achieved at about 0.5 % Mn content.     

Toughening effects of Mo and Nb addition on impact toughness and crack resistance of titanium alloys

Ti-6Al,Ti-6Al-2Mo and Ti-6Al-3Nb alloys were prepared to investigate the toughening effects of β sta-bilizers Mo and Nb on impact toughness and crack resistance of titanium alloys.Instrumented Charpy impact tests showed that the total impact absorbed energy of Ti-6Al-2Mo and Ti-6Al-3Nb (～64J) were two times higher than that ofTi-6Al (～30J),indicating the higher impact toughness of Ti-6Al-2Mo and Ti-6Al-3Nb alloys.Analysis of load-displacement curves revealed the similar crack initiation energy of Ti-6Al,Ti-6Al-2Mo and Ti-6Al-3Nb (15.4J,16.1J and 15.0J,respectively).However,the higher crack propagation energy of Ti-6Al-2Mo and Ti-6Al-3Nb (46.7J and 48.3J,respectively) were about three times higher than that of Ti-6Al (14.4J),indicating the stronger resistance to crack propagation in Ti-6Al-2Mo and Ti-6Al-3Nb.Post-mortem analysis of impact samples demonstrated that the increased dislocation density and deformation twinning were mainly responsible for the stronger resistance to crack propagation in Ti-6Al-2Mo and Ti-6Al-3Nb.Due to the invisibility of dislocation activation and deformation twinning during the Charpy impact process,a mathematical model has been proposed to evaluate the effects of Al,Mo and Nb elements on dislocation mobility based on the Yu Rui-huang electron theory.Addition of Mo and Nb elements significantly improved the dislocation mobility in Ti-6Al-2Mo and Ti-6Al-3Nb compared to that in Ti-6Al alloy.Therefore,more dislocations were activated in Ti-6Al-2Mo and Ti-6Al-3Nb which supplied the larger plastic deformation under impact loading.A dislocation-based model also has been proposed to interpret the nucleation and propagation of deformation twinning under the impact loading.Dislocation pileup at α/β interfaces provided potential sites for nucleation of deformation twinning in Ti-6Al-2Mo and Ti-6Al-3Nb.Furthermore,deformation twinning facilitated the dislocation motion in α grains with hard orientations.The increased dislocation mobility and deformation twinning were responsible for the stronger crack resistance as well as the higher impact toughness of Ti-6Al-2Mo and Ti-6Al-3Nb alloys.     

Mo元素对船用高强钢碱性焊条熔敷金属组织和性能的影响

测试5种不同Mo含量的船用高强钢焊条的熔敷金属力学性能,采用光学显微镜和透射电镜进行微观组织观察和分析,并采用Jamtpro软件模拟计算熔敷金属的焊接CCT图。结果表明,随着Mo含量增多,熔敷金属屈服强度和抗拉强度显著提升,但冲击韧性及塑性呈下降趋势;焊接CCT曲线逐渐向右下方移动,熔敷金属的组织由韧性较好的针状铁素体逐渐向硬脆的贝氏体和马氏体转变;当Mo含量高于0.482%时,熔敷金属中会产生对韧性不利的M-A组元,当Mo含量高于0.887%时,熔敷金属中会析出Mo的碳化物,造成严重脆化。     

Effect of severe plastic deformation on tensile properties and impact toughness of two-phase Zn–40Al alloy

Tensile properties and impact toughness of the severe plastically deformed Zn–40Al alloy were investigated. The material billets were subjected to equal-channel angular extrusion (ECAE). After processing, elongation to failure increased significantly with the increasing number of ECAE passes. ECAE also increased the strength levels after one pass, however, they were reduced with the higher number of passes. The observed softening of the alloy upon multiple ECAE passes was shown to be due to the deformation-induced homogenization and the continuous change in the composition of the constituting phases with the number of passes. In addition, the volume fraction of the hard phase decreased due to dissolution and/or breakage. The impact toughness of the alloy was improved by multi-pass ECAE due to the significant increase in ductility. These findings demonstrate that multi-pass ECAE effectively transforms brittle Zn–Al cast alloys into tougher materials with ductile fracture behavior.     

Impact toughness and fractography of Al–Si–Cu–Mg base alloys

Critical automotive applications using heat-treatable alloys are designed for high impact toughness which can be improved using a specified heat treatment. The alloy toughness and fracture behavior are influenced by the alloy composition and the solidification conditions applied. The mechanical properties of alloys containing Cu and Mg can also be enhanced through heat treatment. The present study was undertaken to investigate the effects of Mg content, aging and cooling rate on the impact toughness and fractography of both non-modified and Sr-modified Al–Si–Cu–Mg base alloys. Castings were prepared from both experimental and industrial 319 alloy melts containing 0–0.6wt% Mg. Test bars were cast in two different cooling rate molds, a star-like permanent mold and an L-shaped permanent mold, with dendrite arm spacing (DAS) values of 24 and 50 μm, respectively. Test bars were aged at 180 °C and 220 °C for 2–48 h. Charpy Impact test was used to provide the impact energy. It was observed that high cooling rates improve the impact toughness whereas the presence of Cu significantly lowers the impact properties which are determined mainly by the Al₂Cu phase and not by the eutectic Si particles. The addition of Mg and Sr were also seen to decrease the impact toughness. The crack initiation energy in these alloys is greater than the crack propagation energy, reflecting the high ductility of Al–Si–Cu–Mg base alloys.     

Toughness and fatigue behaviour of eutectic and hypereutectic Al–Si–Cu–Mg alloys produced through lost foam and squeeze casting

Abstract

The strength and toughness of four high silicon content Al–Si–Mg–Cu alloys have been studied at room temperature (RT), 200°C and 300°C. The fatigue behaviour has also been investigated. The alloys were produced using two very different processing routes: lost foam and squeeze casting. In the tensile tests, the ductility was low for alloys produced via both routes irrespective of the testing temperature. The strength was similar at RT and 200°C, but at 300°C it fell abruptly. The toughness followed the same trend with testing temperature. Direct observation of fatigue cracks revealed that the brittle silicon and intermetallic particles broke ahead of the crack tip; the fatigue crack advanced by linking the main crack with cracks formed ahead of it. The T6 thermal treatment improved fatigue resistance in the squeeze cast material, especially at high D K values.     

Micromechanism of improvement in crack initiation and propagation toughness of a Ti–Al–Sn–Zr–Mo alloy by coarsening prior β-grains

Abstract

Instrumented Charpy V impact tests and static and dynamic fracture toughness tests were carried out on Ti–6Al–2Sn–4Zr–6Mo alloys in which the prior β-grain size was varied by heat treatment. The effect of microstructure on the toughness was then examined. With increasing prior β-grain size, the elongation, crack initiation, and particularly propagation toughness increased and the strength decreased slightly. The increase in crack initiation toughness was caused mainly by the increase in Widmanstätten α-lath size or spacing, while the increase in crack propagation toughness was caused by the deflection of the crack propagation path, which was brought about by the decrease in intersubcolony spacing. The intersubcolony spacing decreased with increasing number of ‘diffusion controlled’ Widmanstätten α nucleating sites, which were introduced by the deformation strain.

MST/786     

Effect of multi-directional forging and ageing on fracture toughness of Al–Zn–Mg–Cu alloys

Strength, ductility and fracture toughness are the most important mechanical properties of engineering materials. In this work, an Al–Zn–Mg–Cu alloy was subjected to multi-directional forging (MF) and ageing treatment. Microstructural evolution was studied by optical and electron microscopy and strength, ductility and fracture toughness were researched. After MF, the dislocation density was increased and the microstructure was refined. The strength and fracture toughness were increased, while the ductility was decreased sharply. Without compromising the strength, the ductility was improved significantly after ageing. The fracture toughness was increased further. The coarse and discontinuously distributed grain boundary precipitates were found to be responsible for higher fracture toughness of the fine-grained structure Al–Zn–Mg–Cu alloy.     

Influence of the thermomechanical processing on the fracture mechanisms of high strength aluminium/pure aluminium multilayer laminate materials

The microstructure and mechanical properties, with emphasis in the impact fracture toughness behaviour, of two multilayer laminate materials have been investigated. The multilayer materials are constituted by alternated sheets of pure aluminium (Al 1200 or Al 1050) and high strength Al 7075 alloy. Stacked layers of these alloys have been successfully joined using two processing routes with different total hot rolling strains. Both laminates have been tested at room temperature under impact Charpy tests, three-point bend tests and shear tests on the interfaces. Both laminates exhibited more than eight times improvement in impact fracture toughness over the monolithic Al 7075-T6. The toughness increase in the higher rolling strained laminate is almost entirely due to crack blunting mechanism, while in the lower strained laminate, crack deflection by delamination and crack renucleation processes were active.     

Thermal aging of 16Cr – 5Ni – 1Mo stainless steel Part 2 – Mechanical property characterisation

Abstract

Mechanical property characterisation has been carried out on specimens of 16Cr - 5Ni - 1Mo stainless steel, subjected to various aging cycles. The heat treatment cycles involved solution treatment at 1050 ° C for 1 h followed by heating in the temperature range 400 - 750 ° C for different holding times (1 - 16 h). After heat treatment, tensile, hardness, impact, and creep tests were conducted. Specimens aged at 475 ° C exhibited maximum values of tensile strength and hardness with minimum values of ductility and impact toughness, while specimens aged at 625 ° C had maximum values of impact toughness and ductility. The results were correlated with the microstructural data presented in Part 1 of this study. Softening of the martensitic matrix at 625 ° C occurs as a result of the elimination of internal stresses, the decrease in the dislocation density, and the high volume fraction of austenite which lead to the drop in values of tensile strength and hardness. The results of the study reveal that aging at 550 ° C for 4 h gives the optimum combination of strength, hardness, ductility and toughness for this steel.