α相形貌对Ti−5Al−5Mo−5V−1Cr−1Fe合金疲劳裂纹扩展行为的影响

采用疲劳裂纹扩展测试、金相显微镜分析和扫描电子显微镜分析方法研究不同α相形貌对Ti−5Al−5Mo−5V−1Cr−1Fe合金的疲劳裂纹扩展敏感性及断裂特征的影响。通过热处理制备的显微组织包括细小和粗大的次生α相组织、魏氏组织和网篮组织。具有粗大次生α相的组织具有最好的综合性能,包括良好的裂纹扩展抗性(Paris区为15~60 MPa·m1/2)、高的屈服强度(1113 MPa)和抗拉强度(1150 MPa),以及良好的伸长率(11.6%)。良好的裂纹扩展抗性归因于粗大次生α相引起的裂纹偏折、长二次裂纹和曲折的裂纹路径。

Characteristics of Faigue Crack Initiation in Ti-5Al-4Sn-2Zr-1Mo-0.7Nd-0.25Si Alloy

The characteristics of fatigue crack initiation in Ti-5AI-4Sn-2Zr1Mo-O.7Nd-O.25Si alloy wereStudied. Two modes Of fatigue crack initiation were found. The Nd-rich phase particles displaybetter resistance to fatigue crack initiation than the matrix at lower stress.

Dynamic response and plastic deformation behavior of Ti–5Al–2.5Sn ELI and Ti–8Al–1Mo–1V alloys under high-strain rate

Split Hopkinson pressure bar test system was used to investigate the plastic deformation behavior and dynamic response character of a-type Ti–5Al–2.5Sn ELI and near a-type Ti–8Al–1Mo–1V titanium alloy when subjected to dynamic loading. In the present work, stress–strain curves at strain rate from 1.5 9 103to 5.0 9 103s-1were analyzed, and optical microscope（OM） was used to reveal adiabatic shearing behavior of recovered samples. Results show that both the two alloys manifest significant strain hardening effects. Critical damage strain rate of the two alloys is about 4.3 9 103s-1, under which the impact absorbs energy of Ti–5Al–2.5Sn ELI and Ti–8Al–1Mo–1V are 560 and 470 MJ m-3, respectively. Both of them fracture along the maximum shearing strength orientation, an angle of 45° to the compression axis. No adiabatic shear band（ASB） is found in Ti–5Al–2.5Sn ELI alloy, whereas several ASBs with different widths exist without regular direction in Ti–8Al–1Mo–1V alloy.

铸造冷作Cr5Mo1V模具钢的合金化与组织性能

采用X射线衍射仪、光学显微镜、扫描电镜和透射电镜等手段,研究了Al含量对Cr5Mo1V模具钢显微组织和力学性能的影响,并分析了Al的作用机理。结果表明,铸态Cr5Mo1V-xAl模具钢的主要物相为α-Fe、γ-Fe和M;C;型碳化物,且随着Al含量增加,模具钢中珠光体面积分数先增大后减小,当Al质量分数增至1.2%时,开始出现δ-Fe相。未添加Al的回火态Cr5Mo1V模具钢中可见板条马氏体和次生碳化物;在Al含量为1.2%和1.5%时,可见局部细小孪晶和粗大碳化物。随着回火态Cr5Mo1V-xAl模具钢中Al含量从0增至1.5%,模具钢的抗拉强度、伸长率、冲击韧度和硬度呈现先增加后减小的特征,适宜的Al含量为1.2%,这主要与此时模具钢中形成了纳米孪晶、较多的次生碳化物和弥散分布的δ-Fe相有关。