【作者】 陈宏涛；

【导师】 闫牧夫；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2008， 硕士

【摘要】 本文对17-4PH钢的表面纳米化工艺,脉冲等离子渗氮工艺进行了研究。通过喷丸、激光表面淬火及喷丸与激光表面淬火复合处理技术,对17-4PH的表面纳米化工艺进行了研究。试验结果表明,激光表面淬火可以在材料表面层获得亚微米级晶粒,喷丸及喷丸+激光的复合处理工艺可以实现材料表面纳米化。通过有无喷丸表面等离子体稀土渗氮试验,得出了渗氮对材料表面硬度及喷丸对渗氮效果的影响规律。不同工艺下的喷丸试验结果表明,选用直径较大的丸粒,采用较大的压强,适当的延长喷丸时间,可以进一步细化表面层的晶粒,获得厚度较大的纳米化表层。XRD结果表明,喷丸可以实现17-4PH钢表面纳米化,最表层约20μm范围内的平均晶粒尺寸为89nm。TEM观察发现,距表面75μm处的亚晶尺寸小于100nm。激光表面淬火研究表明,降低扫描速度,增加功率可以在材料表层获得厚度更大的淬火层;选用适当的功率,增大扫描速度可以提高淬火层的晶粒细化程度;直接激光表面淬火可以在材料表层365μm范围内获得尺寸约1-2μm的晶粒,两次激光淬火可以在材料表层480μm范围内获得亚微米级晶粒;结合喷丸和激光表面淬火工艺特点,利用喷丸与激光表面淬火的复合处理技术,在材料表层获得了230μm厚的从纳米过渡到亚微米级的梯度晶粒。17-4PH在460°C脉冲等离子体稀土渗氮表明,渗氮12h可以在表层获得90μm的渗层,表面硬度约为HV1200。喷丸表面在稀土渗氮前期具有催渗作用,随渗氮时间的延长,催渗作用减弱,渗氮后期阻碍了渗氮。与未喷丸相比,喷丸渗氮显著提高了渗氮表层的显微硬度,可达HV1350。更多还原

【Abstract】 In this thesis, technologies of surface nanocrystallizaition and plasma nitriding of steel 17-4PH have been studied. Shot penning, laser surface quenching and combination of these two technologies have been adopted to study the technology of surface nanocrystallization of steel 17-4PH. The results show that the submicron grain can be obtained by laser surface quenching, and surface nanocrystalization could be achieved by both shot peening and combination of shot peening and laser surface quenching. Pulse plasma RE nitriding carried out with and without shot peening have also been investigated to clarity the effect of nitriding on the surface micro-hardness and the influence of shot peening for nitriding.Results of shot peening with different technologies indicate that: the biger particles selected and the intensity of pressure enlarged, the grain would be even more refined and the layer thickness with refined grain can be deepen. Results from XRD shows that surface nanocrystallization of 17-4PH has been realized by shot peening, the average grain size of the surface layer of about 20μm depth can be 89nm.Results of TEM indicates that the depth of nanocrystal layer reaches 75μm.According to experimental results of laser surface quenching, a deeper quenching layer can be got by bringing down the scanning velocity or increasing the power; while more refined grain in the quenching layer can be obtained by increase the scanning velocity or reduce the power. A layer of 365μm with grain of 1-2μm has been got by direct laser surface quenching, as well as a layer of 480μm with submicron-size grain by twice laser surface quenching. Base on the features of shot peening and laser surface quenching, by the combination of these two technologies, a layer of 230μm with grains of nano-size gradually changing to submicron-size has been achieved.Study on plasma nitriding of steel 17-4PH shows that a nitrided layer of 90μm has been got after nitriding at 460℃for 12 hours and the surface micro-hardness is about 1200HV. It has been also found that pre-shot peening will accelerate the process of nitriding at the initial stage, and this effect will weaken with time, and then will delay the nitriding in the late stage. While nitriding after shot peening will increase surface micro-hardness to about 1350HV compared to nitriding without shot peening.更多还原