导　　师： 沈军

学科专业： 080503

授予学位： 博士

作　　者： ;

机构地区： 哈尔滨工业大学

摘　　要： 本文针对传统铸造法制备Ti基块体非晶合金时合金具有较低的玻璃形成能力的问题，采用不同的焊接方法将小尺寸的Ti块体非晶合金连接成大尺寸的Ti基块体非晶合金，对焊件的微观组织和力学性能进行了系统的研究，并对成功焊接Ti基块体非晶合金的机理进行了探讨。 利用激光焊接技术快速加热和冷却的特点，对不同激光焊接参数下得到的焊件进行了微观组织和性能研究。实验结果表明，在激光功率为3.5kW，焊接速度10m//min时，可以获得完全非晶态的接头，并且该接头的拉伸强度可以达到母材的93/%，体现良好的力学性能，断口表面分布大量脉状花样和熔滴。而在其它焊接参数下得到的焊件，其焊缝区和热影响区内均有晶体相析出。通过计算得出Ti/_/(40/)Zr/_/(25/)Ni/_3Cu/_/(12/)Be/_/(20/)块体非晶合金在加热过程中保持非晶态特征的临界加热速度，该值远远小于激光焊接过程中样品的加热速度，因此，Ti/_/(40/)Zr/_/(25/)Ni/_3Cu/_/(12/)Be/_/(20/)块体非晶合金在加热过程中不会发生晶化。进一步计算得出熔合线附近，靠近焊缝区获得非晶态合金的冷却速度约为780K//s，该值远远大于Ti基块体非晶合金的临界冷却速度，原因在于焊接过程不是在真空条件下进行，大气中的氧显著降低了非晶合金的玻璃形成能力。 采用数值模拟的方法研究了Ti/_/(40/)Zr/_/(25/)Ni/_3Cu/_/(12/)Be/_/(20/)块体非晶合金激光焊接过程中的温度场变化，进一步分析了Ti基非晶合金在激光焊接过程中保持非晶态结构的机理。以高斯面热源＋柱热源为热源模型，考虑对流、辐射的影响，测定了材料热物理参数随温度的变化情况。将模拟计算得到的结果与实验结果相对比，验证了模型的准确性。基于此模型，考察了不同焊接参数下Ti基非晶合金的热历史。结果表明，熔合线附近，靠近焊缝� Due to the limited glass formation ability, Ti-based alloy can be only cast into glassysamples with small size via conventional casting process. In the present dissertation,Ti/_/(40/)Zr/_/(25/)Ni/_3Cu/_/(12/)Be/_/(20/)BMG samples with small-size have been successfully welded intolarge-size Ti-based BMG by different welding methods. The microstructure andmechanical behaviors of welded BMG samples have been systematically investigated.The underlying mechanism for the maintenance of a glassy phase in the welded BMGsample has been also discussed. The microstructures and mechanical properties of BMG samples welded by variousprocessing parameters have been investigated, based on the rapid heating and coolingcharacteristics of laser welding. The results indicated that a joint with fully amorphousfeature could be achieved using a welding speed of10m//min and a laser power of3.5kW. The sound joint exhibits a high tensile strength,93/%of the base alloy,demonstrating a perfect bonding. Well-developed vein patterns, typical of the fracturefeature for amorphous metals, were observed over the whole fractured surfaces. For thecase of the samples welded from other welding parameters, crystalline phases wereobserved both in weld fusion zone and heat affected zone. The critical heating ratekeeping Ti/_/(40/)Zr/_/(25/)Ni/_3Cu/_/(12/)Be/_/(20/)BMG without crystallization during the heating processwas calculated. The calculated critical heating rate was much lower than the heating rateexperienced during laser welding, suggesting that no devitrification occurs duringheating process for Ti/_/(40/)Zr/_/(25/)Ni/_3Cu/_/(12/)Be/_/(20/)BMG. The cooling rate in the weld fusion zonehas been further calculated to be780K//s, much larger than the critical cooling rate ofcast BMG sample. This phenomenon can be attributed to the fact that that the laserwelding was carried out under atmosphere condition. Thus, the introduction of oxygencould seriously suppress the formation of amorphous phase, leading to the highercritical cooling rate for glas

关 键 词： 块体非晶合金 激光焊接 温度场 摩擦焊接 电阻点焊

领　　域： [金属学及工艺] [一般工业技术] [金属学及工艺] [金属学及工艺]