钴及钴基合金拉伸和压缩变形机理的研究现状

Research Status of Tensile and Compression Deformation Mechanism ofCobalt and Cobalt Based Alloys

与镍基高温合金相比,钴基高温合金的高温抗热腐蚀性能、抗热疲劳性能和焊接性等更优越,工作温度更高,因而受到研究者的广泛关注,但高温强度不及镍基高温合金使其应用受限。与传统钴基高温合金相比,新型钴基高温合金由于具有与镍基高温合金相似的γ/γ′共格强化组织而受到人们的青睐,有望替代镍基高温合金,成为新型的合金体系,而进一步提高新型钴基高温合金的拉伸和压缩性能,是拓展合金应用领域必须解决的问题。对纯钴的拉伸和压缩性能已有较详细的报道,纯钴的密排六方晶体结构会导致钴基合金的塑性较差。近年来,研究者们不断地研究如何提高新型钴基高温合金中γ′相的稳定性及拉伸和压缩性能。目前,新型钴基高温合金的延伸率已达到18%左右。新型钴基高温合金压缩变形时出现反常屈服现象是由于螺型位错的交滑移被钉扎,它的驱动力来源于弹性各向异性能和{100}面上较低的反相畴界能。在反常应力峰值附近,位错被限制在γ基体中,偶尔观察到位错切过γ′相。同时,在拉伸加载时也发现了高温反常屈服现象。此外,以三元Co-Al-W合金为基础,通过加入微合金元素(如Mo、Mg、Ce等),可以使新型钴基高温合金的延伸率逐步提高。本文归纳了钴及钴基合金拉伸和压缩变形机理的研究现状。通过介绍密排六方(HCP)金属钴的滑移变形、孪生变形以及钴的变形机制和不同形变孪晶的特征,以钴基合金的塑性变形机理为主线,重点对钴基高温合金的压缩和拉伸变形,特别是由γ/γ′共格强化的钴基高温合金的反常流变应力,及在室温和高温拉伸条件下合金的塑性变形和破坏模式进行阐述。最后,提出了新型钴基高温合金塑性变形方面有待解决的问题。

Cobalt-based superalloys are superior to nickel-based superalloys in terms of their high temperature thermal corrosion resistance,thermal fatigue resistance and weldability.Their working temperatures are higher,which is widely concerned by researchers.However,its high tempe-rature strength is lower than that of nickel-based superalloys,which limits its application range.Compared with traditional cobalt-based superalloys,the new cobalt-based superalloys are favored by people because of theirγ/γ′coherent strengthening structure similar to the nickel-based superalloys.It is expected to replace nickel-based superalloys and become a new alloy system,but further improvement of the tensile and compressive properties of the new cobalt-based superalloys is a problem that must be solved in expanding the application of alloys.The studies on the tensile and compressive properties of pure cobalt have been reported in detail.The recent years,researchers have been constantly researching how to improve theγ′phase stability of new cobalt-based superalloys,as well as the tensile and compressive properties of the alloy.At present,the elongation of the new cobalt-based superalloys has reached about 18%.The abnormal yield phenomena of a new cobalt-based superalloy is caused by the cross-slip of screw dislocations pinned in the compression deformation.Its driving force is derived from the elastic anisotropy energy and the lower anti-phase boundary energy(APB)on{100}plane.Near the peak value of abnormal stress,dislocations are confined to theγmatrix,and occasionally the dislocations cut through theγ′phase are observed.And abnormal yield phenomena is also found under tensile loading at high temperature.In addition,based on ternary Co-Al-W alloy,the elongation of the new Co-based superalloy can be gradually improved by adding micro-alloying elements,such as Mo,Mg,Ce,etc.This paper summarizes the research status of the tensile and compressive deformation mechanism of cobalt and cobalt-based alloys.By introducing the slip deformation,twinning deformation,deformation mechanism and the characteristics of different deformation twins of close-packed hexagonal(HCP)cobalt metal.The plastic deformation mechanism of cobalt-based superalloys is taken as the main line,and the compression and tensile deformation of cobalt-based superalloys are emphasized,especially the anomalous flow stress of cobalt-based superalloys streng-thened byγ/γ′conformity,and the plastic deformation and failure modes of alloys under room temperature and high temperature tensile conditions are described.Finally,the problems to be solved are put forward in the plastic deformation of the new cobalt-based superalloy.