【作者】 王书杰；

【导师】 苏彦庆；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2008， 硕士

【摘要】 液态置氢技术是将氢气或者钛氢化合物直接置入液态金属中去的全新的氢处理方法,是一种新方法,新手段。本文研究了液态置氢吸氢行为;通过金相显微镜、扫描电镜、透射电镜研究了液态置氢后钛合金的宏观组织和微观组织的变化;通过Gleeble-1500热模拟机、万能材料试验机和显微硬度计测试了液态置氢后的力学性能变化。研究结果表明:置氢的量随着氢分压力的增加而增加,最大置氢量可以达到10at.%;液态置氢的时间极短,对于29克的钮扣锭约为100s以内。Ti600合金液态置氢后,发现组织先细化后又长成粗大的柱状晶;TC21合金随着氢含量的增加组织细化趋势明显,并生长成细小柱状组织。通过理论分析认为细化由于形核率的提高和枝晶游离造成的,氢元素降低了临界晶核表面自由能;降低扩散激活能,氢增强了钛原子的自扩散能力和溶质原子的扩散能力;从而增加了熔体的形核率;晶粒的游离是由于氢原子促近了枝晶的产生及其枝晶根部的颈缩和重熔。柱状组织的产生是由于氢电弧促使熔体表面温度过高造成的。组织的形态是由两者竞争形成的,可见氢对组织的形态有重要影响。Ti600合金液态置氢后,α板条变得细小,当加氢至6.2at.%时组织中出现了α′马氏体和β相,当加氢至10.0at.%时,合金中发现有β相、α′马氏体、β相和γ(面心四方结构)氢化物生成。TC21合金液态置氢后,α′板条变得细小,当加氢至6.5at.%时形成了α"相马氏体,随着加氢量的增加α"相增多,加氢至9.2at.%时形成了孪晶α′相。液态置氢使得Ti600和TC21两种合金的流变应力和屈服强度降低,10at.%左右的氢可以使得两种合金的流变应力和屈服强度降低25%左右。氢的加入降低了变形温度和提高了应变速率。Ti600和TC21两种合金随置氢的增加,流变应力和屈服强度随着温度降低的趋势变缓。Ti600钛合金随着置氢量的增加硬度上升,这是由于合金中的α板条变得细小并且氢含量较高时有α′马氏体和γ氢化物生成使得合金硬度增加,尽管这里有β相生成。TC21钛合金随着置氢量的增加硬度下降,这是由于合金中的β相增多,并且有较软的α"相生成。更多还原

【Abstract】 The technology of liquid state hydrogenation for titanium alloy is a new means which directly add hydrogen or TixHy into liquid state titanium alloy. In the paper, The hydrogenation behavior were studied. Optical microscope (OM), scanning electron microscope(SEM) and transmission electron microscope (TEM) were used to study the influence of hydrogen on the microstructures and macrostructures. Ti600 and TC21 alloy are compressed inα+βandβphase field on a Gleeble-1500 Simulator and Universal Testing Machines. Their hardness is tested by Micro Hardness Tester.Experimental results showed that the amount of hydrogen absorbed in titanium alloy is increasing with the pressure of hydrogen and the process is accomplished only in 100s for 29g titanium alloy of liquid state and the most the amount of hydrogen absorbed in titanium alloy is about 10.0at.%H.As increase of hydrogen desorbed in liquid state of Ti600 titanium alloy, the macrostructures was refined at the first, then it become a kind of coarse columnar crystal. But TC21 is from a kind of coarse equiaxed structure to fine columnar crystal. According to solidification theory, the improvment of nucleation rate and dendrite fragmentation is contributed to the refinement of Ti600 and TC21. In addition, it is a main reason for columnar structure that hydrogen promote superheat of melt surface. So, the macrostructures conformation is a result of competition of refinement and superheat of melt surface.After hydrogenated for Ti600,αlamellar was refined. There areβandα′martensite found in the specimen containning 6.2at.%H andγtitanium hydride precipitated in the specimen containning 10.0at.%H as well asβandα′martensite.After hydrogenated for TC21,α′martensite was refined, orthorhombic martensiteα" was found in the specimen containning 6.5at.%H and the content ofα" martensite increases with hydrogen.Hydrogen absorption in titanium alloys could decrease the flow stress and high temprature yield strength of titanium alloys, 10at.% of hydrogen can decrease about 25at.% of the flow stress and high temprature yield strength of titanium alloys. Therefore, hydrogen may reduce the requirement of deformation temperature and strain rate for plastic forming. With increase of the content of hydrogen, sensitivity of the flow stress and high temprature yield strength for hydrogen is decreased.The hardness of TC21 alloy is continuously decreased with increasing hydrogen content due to the effect of the softβandα" phase. However, the hardness of Ti600 alloy is continuously increased with increasing hydrogen concent due to the refinement of theαlamellar and the appearance ofα′martensite andγtitanium hydride.更多还原