再结晶厚度对定向凝固DZ125合金蠕变性能的影响

Effect of RecrystallizationThickness on Creep Propertiesof Directional Solidified DZ125 Alloy

摘要:

柱状晶DZ125合金在铸态条件下进行不同强度的表面吹砂,然后进行标准热处理获得不同厚度的再结晶层,并测定出合金的蠕变寿命,对比分析再结晶及其厚度对合金蠕变性能的影响,采用扫描电镜对铸态、热处理态和蠕变断裂后合金的微观组织进行观察,试验结果表明：柱状晶DZ125合金在不同吹砂强度条件下,热处理后合金表面发生再结晶厚度不同,随吹砂强度的增大再结晶层的厚度增大。铸态DZ125柱状晶合金中的碳化物呈片状、条状或颗粒状,经标准热处理后合金中的碳化物部分发生溶解,片状碳化物尺寸减小,碳化物表面出现孔洞,条状碳化物转变为颗粒状,原有颗粒状碳化物尺寸降低。再结晶后,晶界析出少量颗粒状碳化物。具有不同再结晶厚度的2mm和4mm片状试样,在980℃/235MPa条件下的蠕变寿命相当,与未发生再结晶的柱状晶合金相比寿命降低30%。蠕变期间再结晶晶界碳化物发生了积聚和长大,这有利于提高再结晶晶界强度。蠕变期间断裂裂纹主要沿与应力轴垂直的再结晶晶界萌生,在柱状晶合金内部也存在裂纹萌生点。再结晶晶粒内发生了γ′相筏形化,说明柱状晶再结晶晶界虽然弱化了合金的蠕变强度,但其本身也具有一定的强度。

Abstract:

The surface of as-cast columnar crystal DZ125 alloy was blew sand then heat treatment by the standard heat treatment process obtained the recrystallization with different thickness, and the creep life of the alloy was measured. The effect of recrystallization and its thickness on the creep properties of the alloy was analyzed. The microstructure of the alloy was observed by scanning electron microscope. The experimental results show that the thickness of recrystallization on the surface is different from alloys at varied sand blowing intensity after heat treatment, with the sand blowing intensity increase the thickness increase of the columnar crystal DZ125 alloy. The carbide in the as cast DZ125 columnar crystal alloy is slice, strip or grain, and the carbide after the standard heat treated alloy is dissolved, the size of the slice is reduced, and the surface of slice carbide appears holes. Strip carbides turn into grain, the original grain size reduction. A small amount of grain carbides are precipitated around the grain boundaries after recrystallization. The creep life of 2mm and 4mm sample with different recrystallization thickness is roughly equal under the 980℃ and 235MPa conditions. Compared to the non-occurrence the recrystallization of columnar crystal alloy, the life of the DZ125 alloy was decreased by 30%. During the creep, the carbides in the grain are accumulated and grow around the grain boundary, which is beneficial to improve the strength of grain boundary. During creep the crack initiation is mainly along with the recrystallization grain boundary which vertical the stress axis. Crack initiation points are also existed in the internal of the columnar crystal alloy. The γ′ phase rafted in recrystallization grains indicate that the grain boundaries of recrystallization which weakening the creep strength of the alloy also has certain strength.