时效时间对铸态Fe56.5Ni30Al10.5Nb3形状记忆合金组织与性能的影响

Effect of aging time on microstructure and properties of as-cast Fe56.5Ni30Al10.5Nb3 shape memory alloy

研制一种无Co添加的Fe56.5Ni30Al10.5Nb3(atom fraction/%)合金,在制备中直接对铸态合金进行固溶和650℃下的时效处理。利用扫描电子显微镜(SEM)和X射线衍射仪(XRD)分析合金的组织和物相,同时对其进行硬度测试、抗压强度测试、超弹性测试及电子背散射衍射(EBSD)测试。结果表明:时效时间处于0~95 h的范围时,合金内均能析出纳米尺寸的γ′相和细小的β相,在室温都展现出超弹性,最大超弹性应变达10.62%;γ′相在晶内析出,在时效时间为70 h时分布最密集,时间超过70 h后进入长大阶段;β相在晶内和晶界都能析出,析出量随时效时间的延长而增加;β相的析出能促进硬度的增加,但其在晶界的生成对强度不利;随着时效时间的延长,合金硬度持续增加,抗压强度和超弹性应变均先增加后减小,且均在时间为70 h时取得最大值;合金内部纳米尺寸的γ′析出相及较强的{100}<001>织构对其超弹性影响较大。

A Co-free Fe56.5Ni30Al10.5Nb3(atom fraction/%)alloy was developed.In the preparation,the as-cast alloy was subjected to aging treatment at 650℃and followed solution treatment directly.Scanning electron microscope(SEM)and X-ray diffractometer(XRD)were used to analyze the microstructure and phases of the alloy.At the same time,the hardness test,compressive strength test,superelasticity test and electron backscatter diffraction(EBSD)test were performed.The results show that,when the aging time range from 0 to 95 h,the alloy can exhibit superelasticity at room temperature with the maximum superelastic strain of 10.62%.There are nano-sizedγ′precipitates and fineβprecipitates in the alloy.Theγ′phase is formed in the grain interiors and is most densely distributed when the aging time is 70 h.After the aging time exceeds 70 h,theγ′phase enters the growth stage.Theβphase can be formed both in the grain interiors and in the grain boundaries,and the amount ofβprecipitates increases with the aging time.The precipitation of theβphase can improve the hardness,but its formation in the grain boundaries is detrimental to the strength.With the increase of aging time,the hardness of the alloy increases continuously,and the compressive strength and superelastic strain first increase and then decrease,and reach the maximum value at the time of 70 h.The nano-sizedγ′precipitates and strong{100}<100>texture in the alloy have a great influence on its superelasticity.