Fatigue Strength and Fracture Mechanisms in Intermetllic Compound Particlate-Reinforced

通过静态力学性能和疲劳性能的评价以及金相观察，发现金属间化合物NiAl和Ni3Al颗粒增强铝压铸件优于碳化硅增强铝压铸件。室温强化提高了耐久极限。而胎体压铸和碳化硅颗粒增强的耐久极限随着温度的升高而降低，NiAl在200ﾟC和Ni_3Al颗粒在300ﾟC以下强化效果最好。在所考察的所有温度范围内，耐久极限和疲劳寿命都随着颗粒体积分数的增加而增加。虽然这些特性基本相当于0.2%的抗应力，但金属间化合物颗粒与Al_3Ni等析出物共同抑制局部滑移对低应力下的疲劳强度有显著贡献。疲劳裂纹在…表面附近的空洞处萌生在所有压铸件中介绍了更多关于铸造的内容。裂纹通过基体并沿颗粒-基体界面扩展，在高温下前者占主导地位。Ni_3Al颗粒中未发现裂纹。2.5Vol%NiAl颗粒增强压铸件的疲劳裂纹扩展抗力在近门槛值区高于基体和碳化硅增强压铸件。当粒子体积折射率增加到2.5%以上时，它会减小。在Paris规则或更高的裂纹扩展速率范围内，2.5%NiAl颗粒增强压铸件具有较高的裂纹扩展阻力，而碳化硅的裂纹扩展阻力较低，这些特性与断裂韧性的特性不一致。NiAl颗粒增强压铸件具有良好的抗两阶段(低-高和高-低)变应力疲劳特性。金属间化合物颗粒增强压铸件疲劳裂纹在间歇过应力作用下的加速扩展及其微观机制是一个悬而未决的问题。较少

Through the evaluation on static mechanical properties and fatigue characteristics as well as the microscopiic observations, it has been revealed that the intermetalic compund, NiAl and Ni_3Al, particle-reinforced Al die cast are superior to the SiC reinforced one as is shown in the followings.1. The endurance limit increases by reinforcement at room temperature. While the endurance limit ofmatrix die cast and SiC particle reinforced one decrease with temperature rise, reinforcement is effective at 200ﾟC in the NiAl and up to 300ﾟC in Ni_3Al particle. The endurance limit and fatigue life-time increase with increase in the particle volume fraction in all temperature ranges examined. Although these characteristics basically corresponds to that of 0.2% proof stress, suppression of local slip by the intermetalic compound particles together with precipitates such as Al_3Ni significantly contribute the fatigue strength at low stress.2. Fatigue crack initiates at voids located near the surfac … More e which are introduced on casting in all die casts. Crack propagates through the matrix and along the particle-matrix interface, and the former is dominant at elevated temperatures. No cracking in Ni_3Al particle is found.3. Fatigue crack propagation resistance of 2.5 vol% NiAl particle reinforced die cast is higher at near threshold region than the matrix and SiC reinforced one. It decreases when the particle volumefraction increase beyond 2.5%. In the crack propagation rate range of Paris rule or beyond it, 2.5 vol% NiAl particle reinforced die cast has higher crack propagation resistance while SiC has such low resistance as that in the matrix : These characteristics dose not coinside with that of fracture toughness.4. NiAl particle reinforce die cast has excellent fatigue characteristics against the two stage (low-high and high low) varying stress fatigue. Acceleration of fatigue crack propagation under intermittent oversrtressing and its microscopic mechanism in the intermetalic compound particle reinforced die cast is open problem. Less