Inconel 740H合金原位高溫拉伸微裂紋萌生擴(kuò)展研究

Inconel 740H合金原位高溫拉伸微裂紋萌生擴(kuò)展研究Microcrack nucleation and propagation investigation of Inconel 740H alloy under in stiu high temperature tensile test

利用自主研發(fā)的掃描電子顯微鏡原位高溫拉伸臺(tái)，研究了750℃高溫條件下鎳基高溫合金Inconel 740H單軸拉伸變形過程中微觀組織演變規(guī)律及微裂紋萌生與擴(kuò)展機(jī)制。結(jié)果表明，在室溫和高溫條下，Inconel 740H合金受力變形過程中晶界是主要的裂紋萌生源，但是在室溫時(shí)微裂紋也會(huì)在晶內(nèi)萌生。通過對(duì)原位變形機(jī)制分析表明，750℃高溫不僅降低了滑移系的開啟能量，使更多的滑移系容易開動(dòng)，而且弱化了晶界強(qiáng)度，使晶界具有彎曲和滑移的變形特性，從而增強(qiáng)了合金的塑性變形能力，但是降低合金的屈服強(qiáng)度和抗拉強(qiáng)度，高溫作用也使合金晶界相對(duì)強(qiáng)度的弱化又導(dǎo)致微裂紋更易從晶界處萌生并擴(kuò)展。

In this paper, the microstructure evolution and the nucleation and propagation mechanisms of microcracks in the nickel base superalloy Inconel 740H under 750 ℃ high temperature were studied by the self-developed in-situ high temperature tensile stage inside a scanning electron microscopy. The results showed that under the uniaxial tensile stress at 22℃ room temperature and 750℃ high temperature conditions, the grain boundaries of Inconel 740H alloy are always the most primary crack sources. The strength of grain boundarise is higher than that of grains under the room temprature, and the microcracks will be nucleated at the grains as well, but the relative strength of grain boundaries will be weaken under the high temperature, which makes the microcracks tend to nucleate at grain boundaries. The experimental results also showed that the influence of high temperature on the mechanical properties is very significant, the high temperature reduceing the activate energy of slip and weakening the strength of the grain boundaries, so that more slip systems activated and the grain boundaries occurring bending and sliding deformation, so further enhance the ability of plastic deformation of alloy. However, the reduction of relative strength of alloy grain boundaries leads to microcracks nucleation and propagation more easily from grain boundaries and lower the yield strength and tensile strength of alloy.

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