钛基合金温压成形技术研究

【作者】 何世文；

【导师】 欧阳鸿武；

【作者基本信息】 中南大学 ， 材料学， 2004， 硕士

【摘要】 近年来，低成本高性能粉末冶金钛合金逐步成为国际上新材料研究的重要内容。为此，以纯Ti粉和TC4粉末为原材料，对钛合金粉末温压成形行为和粉末表面堆积形态对压坯致密化的影响进行研究，探讨在较低压制压力下制备高性能粉末冶金钛合金的可行途径。 对钛合金粉末的温压特征及其致密化机理的研究结果表明，在同一压制压力下，Ti粉或TC4粉的压坯密度均在温压温度为140℃左右达到最大值，高于或低于这一温度，压坯密度反而下降。压制压力与压坯密度之间的关系和川北公夫压制方程相吻合。在500MPa压力下，温压成形的Ti粉压坯密度为3.72g．cm^-3，比室温成形的增加0.21g．cm^-3；温压成形的TC4压坯密度达3.62g．cm^-3，比室温成形的提高0.18g．cm^-3。并且，在压力为500MPa成形时，温压成形的脱模力比室温成形的脱模力降低约26％。 通过对钛粉的动态压制曲线、脱模力曲线、X射线衍射、显微硬度和压坯显微组织等分析，认为钛粉的温压致密化机理：在温压初期阶段，粉末的重排占主导地位，其对致密化的贡献明显高于室温成形，而在后期温压致密化以塑性变形为主，温度对钛粉塑性变形程度的改善又为粉末颗粒的二次重排起到了协调作用，使钛粉获得更大程度的颗粒填充密度。 为了进一步改善钛合金温压过程的粉末流动性，提高压坯密度及其均匀性，采用MSC．Marc2001软件，数值模拟了钛粉呈平式、凹式、凸式3种不同粉末表面堆积形态的压制过程，并进行了相应的实验验证。结果表明，凸式打破了平式压制过程中粉末移动困难的局面，无论轴向和径向，都产生了比平式更显著的运动，在提高压坯密度的同时，还有效地提高了压坯密度的均匀性。 根据钛粉的特点，将粉末表面凸式堆积应用于钛粉温压成形技术，在500MPa压力下，钛粉的压坯密度达3.87g．cm^-3，比传统的室温成形提高0.27g．cm^-3，增幅达7.5％。这为低成本高性能粉末冶金钛合金的制备探索了一条新的途径。更多还原

【Abstract】 It is vital to manufacture lower cost, high performance titanium-based powder metallurgy materials. In this thesis, warm compaction and the surface shape of loading powder have been studied. Powder designed for warm compaction is fabricated from titanium powder and Ti-6A1-4V powder.Both characteristics and densification mechanism of warm compaction have been researched. The results show that the green density does not increase linearly with compaction temperature. At the optimum temperature of 140℃, the green density will be highest. The compacts density of titanium powder and Ti-6A1-4V powder by warm compaction can reach 3.72g.cm-3 and 3.62g.cm-3 respectively after being pressed at 500MPa. Compared to room compaction, the increase in green density are 0.21and 0.18 g.cm-3, respectively. The relation of green density and compression force is consistent with Kawakita’s powder compaction equation in warm compaction. The ejection force of warm compaction is 26% lower than that of cold compaction after being pressed at 500MPa.Researches on the dynamic compacting curve of titanium powder, ejection force curve, X-ray diffraction, micro-hardness and microscopic structure of compact results show the densification mechanism of warm compaction: during the initial stage, the rearrangement of powder particles is the main factor which contribute more to the densification of warm compaction than to that of cold compaction; during the later stage, the plastic deformation is primary, and the improvement of plastic deformation by temperature can harmonize the second rearrangement of powder particles.With the aid of MSC.Marc 2001 Software, a numerical simulation of compaction on titanium powder has been researched. Results show that the powder movement of the convex model is more obvious than that of the level model. The former improves uniformity of density distribution.When the warm compaction combined with the convex model, the compact of titanium powder with density up to 3.87g.cm-3 can beachieved after being pressed at 500MPa. The increase in green density is 0.27g.cm"3 over conventional compaction. It is considered a new way of a lower cost to produce high performance powder metallurgy titanium alloys.更多还原