回火处理对一种新型钴基合金表面结构和压缩力学性能的影响

Effect of Temper Treatment on the Surface Structure and the Compressive Mechanical Properties of a New Cobalt-based Alloy

本文对钴基合金试样进行了不同时间的回火处理,对压缩应力-应变曲线进行了分析,通过对回火前后钴基合金的微观组织和断口形貌的扫描电镜观察,解释了该钴基合金回火处理前后的压缩断裂过程变化和压缩性能差异。研究发现,回火处理前后的压缩试样断裂过程有较大差异:未经回火处理的试样,其压缩断裂过程表现为典型的脆性断裂,断裂面与压缩方向呈45°夹角;而经过回火处理的压缩试样,首先在试样表面产生平行轴线方向的裂纹,同时在试样顶端形成一个45°锥形断裂面,最后试样断裂。回火过程中生成的氧化层是回火试样压缩断裂过程变化的主要原因,但是对整个压缩曲线的变化起主导作用的仍然是材料的基体组织。回火后的钴基合金组织中fcc-Co相比例显著增加,Cr_(23)C_(6)碳化物颗粒尖角消失,形状变得圆滑,显著改善了该钴基合金的韧性。

In this paper,the compressive properties and the fracture process of a cobalt-based alloy before and after tempering were analyzed and explained.The compression stress-strain curves before and after tempering were analyzed.The microstructures of the cobalt-based alloy were investigated by using X-ray diffractometer(XRD)and scanning electron microscope(SEM).The fracture process of the compressed samples before and after tempering treatment is very different.The fracture process of the compressed samples without tempering treatment is a typical brittle fracture,exhibiting an angle between fracture surface and compression axis direction of 45°.After tempered treatment,the crack was firstly generated at the surface of the compressed sample.The cracking direction was parallel to the compression direction.At the same time,there was a 45°conical fracture surface formed on the top of the sample,and then the sample fractured under compression.The core-shell structure formed by oxidation during tempering is responsible for the change of the compressive fracture behavior of this cobalt-based alloy.However,the microstructure of the material itself played a dominant role in the whole compression process.After tempering,the content of fcc-Co phase in the Co matrix obviously increased and the sharp angle of Cr_(23)C_(6) particles disappeared and became smooth,which improved the toughness of the cobalt-base alloy.