【作者】 蔡方寒；

【导师】 唐霞辉；

【作者基本信息】 华中科技大学 ， 物理电子学， 2005， 硕士

【摘要】 本文采用高功率CO2激光器,对青铜-钛、青铜-钴-镍金属粉末与金刚石颗粒进行了激光烧结试验研究,旨在探索制备异形金刚石工具及其新型复合材料的新方法。首先,通过试验研究发现,在保持光斑直径D=8.5mm,压坯厚度0.7～1.0mm,氩气流量恒定时:(1)青铜-钛金属粉末在激光烧结过程中极易氧化,表面残渣结瘤现象严重。(2)以青铜-钴-镍为主的金属粉末具有良好的激光烧结性能:①在较高激光能量输入时,烧结件微观组织为铸态“鱼骨状”类枝晶组织;在较低激光能量输入时,组织疏松,以颗粒团聚为主;在过高激光能量输入时,烧结过程变成液相烧结。②烧结件断口呈现“窝形”特征,属典型韧性断裂行为。③在一定范围内,扫描速度保持不变时,随着激光功率的提高,烧结件致密度和耐磨性能提高;激光功率保持恒定时,随着扫描速度提高,烧结件致密度降低,耐磨性能提高。而激光功率、扫描速度和线能量对烧结件抗拉强度的影响规律都具有高斯分布特征。在极值点w≈42J/mm 可获得抗拉强度最佳的烧结件。然后,本文从理论上深入分析研究了金刚石颗粒间断条件下的金属粉末激光烧结致密化行为以及金刚石与金属结合机理:(1)金属粉末压坯激光烧结致密化行为主要是低熔点元素形成液相、高熔点元素微熔以及元素扩散形成固溶体。(2)强碳化物形成元素Cr、Fe、Co 等向金刚石偏析富聚,使得部分液相以金刚石为形核凝固,在金刚石表面形成轻微的冶金结合,镀钛金刚石周围还有Cu 偏析。本文着重分析研究了高能激光束作用下金刚石损伤和烧结气孔等缺陷:(1)金刚石的损伤主要是烧损氧化和石墨化。在较高激光输入能量下,金刚石颗粒主要出现晶形破坏和轻微的烧损氧化;在过高激光输入能量下,同时可以观察到金刚石严更多还原

【Abstract】 In this thesis, CO₂ laser sintering experiments of bronze-Ti and bronze-Co-Ni powder with diamond grits have been done, aiming for exploring the new technique of manufacturing peculiar-shaped diamond tools and new synthetic material. Firstly, the technique of laser sintering has been studied, while keeping focus diameter 8.5mm, thickness of compact 0.7¹.0mm and constant flow of Ar gas, the results showed as follows: （1） During laser sintering, the bronze-Ti powder is oxidized most easily and plenty of residua and lump is observed. （2）The bronze-Co-Ni powder has outstanding performance of laser sintering: ①Under the high laser energy input, the microstructure of casting state and fishbone shape similar to branch crystal is observed. Under the low laser energy input, the microstructure is very loose and the grains gather and felt together. But when the laser energy is excessively high, laser sintering turns into liquid-phase sintering. ②Lots of sockets exist in the fracture of sintered samples, so it is typical fracture with toughness. ③In a certain range, while keeping constant scanning speed, the density and abrasive resistance of sintered samples are raised with the increase of laser power. While laser power is constant, the density are decreased and the abrasive resistance raised with the increase of scanning speed. But the relation of laser power, scanning speed and linear energy with the stretch intensity shows the characteristic of Gauss function. And when the linear energy is about 42J/mm, the sample with the optimal stretch intensity will be obtained. Secondly, the densification of metallic powder with diamond grits during laser sintering and the mechanism of combination between metallic powder and diamond grits have been analysed and studied in theory: （1） The densification of metallic powder compact during laser sintering includes three steps: the low melting point metal melted, high melting point metal melted slightly and atoms diffused. （2） The metal which reacts to C easily such as Cr, Fe, Co, gathers around the diamond grits, which makes much liquid solidify around the diamond nucleus and forms metallurgical combination on the surface of diamond. On the surface of Ti-coated diamond grits, Cu exists. Finally, the thesis emphasizes on study of the defect of high power laser sintering, such as the damnification of diamond grits and pore: （1） The damnification of diamond grits mainly includes oxidation and carbonization. Under high laser energy input, shape of diamond grits are destroyed and grits are oxidized slightly. But under excessively high energy input, the diamond grits are not only oxidized seriously, also carbonized to loose graphite slice. （2） Coating Ti on the surface of diamond grits will increase capacity of combination between diamond and metallic powder, and resistance of damnification. （3） The pore is induced mostly by air remained in the compact, and gas which is formed during oxidization of diamond. The thesis has researched systematically the technique and mechanism on high power laser sintering of metallic powder with diamond grits for the first time and pioneered the new field of laser sintering application. It is important and instructive for the manufacture of big area peculiar-shaped diamond tools and new synthetic material.更多还原