共查询到19条相似文献,搜索用时 60 毫秒
1.
2.
3.
4.
5.
6.
7.
零件渗碳后渗层的碳浓度分布可以用有限差分法预测,而碳浓度的高低决定了工件淬火后的硬度。根据试验数据建立了马氏体含碳量与硬度的函数关系,预测了圆柱形工件渗碳后的碳浓度分布和淬火后的硬度,硬度的预测结果与试验结果相吻合。 相似文献
8.
9.
在对高浓度深层渗碳的特点进行分析的基础上,考虑到碳化物的析出与溶解、温度及碳浓度对扩散行为的影响,气氛环境对相界面碳传递过程的影响,淬火烈度对渗碳层冷却效果的影响,提出了一种新的模拟高浓度深层渗碳渗层硬度分布的方法。 相似文献
10.
用有限单元法对齿条及工件的尖角部位渗碳浓度场进行计算机模拟,计算结果以等浓度曲线形式直观表示。在模拟结果的基础上,可根据工件的服役条件进行渗碳工艺优化设计,对于改善渗碳件的碳浓度分布提高渗碳工件的使用寿命定能提供很大帮助。 相似文献
11.
12.
This paper presents a new model for simultaneous diffusion and precipitation of chemical elements in metallic matrices, a scheme for its numerical solution, and several applications to problems of internal oxidation. The model basically stands as an extension of the classical Wagner model for internal oxidation of steels, but is more much general in that it allows for an arbitrary number of diffusing chemical elements, an arbitrary number of precipitate phases with arbitrary compositions, dependence of diffusion coefficients and solubility products upon (time-dependent) temperature, etc., thus allowing for a much broader range of applications. As a counterpart, it is generally impossible to solve the complex, non-linear equations of the model analytically, but this can be done numerically. The simple but efficient numerical scheme proposed is based on explicit 1D finite differences. Experience has shown that this scheme, in spite of its rusticity and the restrictions it imposes on the time-step, is more efficient than more elaborate strategies based on the finite-element method. The applications presented are concerned with internal oxidation of steels during annealing processes. The model and associated numerical scheme allow for evaluation of the amounts of the various oxide precipitates in the external layer of the sheet. This opens the way, through numerical parametric studies of the influence of the process parameters and the chemical composition, to the improvement of existing treatments and the development of new steel grades. 相似文献
13.
A series of 21 commercial austenitic heat-resistant alloys was carburized in H2-C3H6 atmospheres which were reducing to Cr2O3 and SiO2 and which provided a carbon activity of one. Reactions were carried out at 900T1100°C and the resulting depth of carburization was measured metallographically. All alloys showed parabolic carburization kinetics after an initial brief period, at low temperatures, of more rapid reaction. The apparent activation energies for carburization are discussed in terms of carbon solubilities and diffusion coefficients. It is concluded that Wagner's theory of internal oxidation is quantitatively applicable to simple alloys but not to alloys which contain additions of reactive elements. The effectiveness of additions of niobium, aluminum, titanium, and silicon is demonstrated and is discussed in the context of Wagner's theory. 相似文献
14.
针对己预腐蚀生成一定厚度氧化膜的Zr-Sn-Nb合金,研究了其在不同温度下进行真空热处理过程中的氧扩散动力学及亚稳相演变行为.结果表明,真空退火后氧化膜变薄,氧在氧化锆基体中的扩散增强,并计算了特定合金中氧的扩散系数.退火后微观化学分析表明亚稳相层厚度增加.固溶氧锆基体(Zr(O))层也明显增厚.针对该现象,讨论了对应... 相似文献
15.
用无缺口和有缺口试样研究了几种渗碳钢的静弯特性和冲击特性,结果表明,渗碳层由表及里成分和组织的变化使缺口深度性能的影响规律复杂化,塑性和韧性越差的钢其缺口脆化作用越小,从而使缺口性能上的差异比无缺口时性能上的差异变小,从静弯强度,挠度,弹塑性功,裂纹扩展功以及缺口冲击韧性等几个方面综合考虑,20Cr2Ni4A和17CrNi2Mo钢的性能优异,20CrMnTi钢较差,性能最差的是20CrMnMo钢, 相似文献
16.
强化均匀化对7B04铝合金铸态组织与性能的影响 总被引:8,自引:4,他引:8
研究了强化均匀化 (大幅度延长均匀化时间 ,略高于传统均匀化温度 )对 7B0 4铝合金铸态组织和性能的影响。结果表明 :在 4 6 8℃× 4 8h的均匀化制度下 ,材料的铸态组织得到明显的改善 ,非平衡凝固形成的多相组织基本上转变成均匀化组织 ,材料的伸长率较传统均匀化提高 14 % ,为后续压力加工和热处理奠定了基础。 相似文献
17.
表面扩渗Al,Zn处理对ZM5镁合金性能的影响 总被引:8,自引:0,他引:8
通过铝锌(Al,Zn)混合粉对ZM5镁合金进行了表面固态扩渗铝锌(Al,Zn)处理,在衬底形成了Mg-Al-Zn合金层.研究结果表明:Mg-Al-Zn合金层主要由Mg-Al-Zn固溶体和Mg-Al-Zn金属间化合物(Al6Mg10Zn,Al5MgllZn4)组成,该合金层不仅使ZM5镁合金表面合金层显微硬度显著提高,而且在盐水浸泡腐蚀过程中,在衬底与腐蚀介质之间起到了良好的屏障作用,从而赋予试样良好的腐蚀性能. 相似文献
18.
研究了渗碳处理对Ti-34wt%Al二元合金抗氧化性的影响,试验结果表明,表面渗碳处理能够有效地提高TiAl基合金的抗氧化性。 相似文献
19.
目的通过表面固态扩渗合金化技术获得金属扩渗涂层,研究扩渗涂层的形成机理。方法在390℃对AZ81镁合金表面固态扩渗Al和Zn,通过X射线衍射仪和光学显微镜,对扩渗合金层的物相结构和形貌进行分析,通过建立扩渗过程模型研究其扩渗形成机理。结果扩渗时间为4~8 h时,合金扩渗层中除了AZ81镁合金的原始相a-Mg+Mg_(17)Al_(12)外,还会发生Mg_(0.97)Zn_(0.03)→Mg_7Zn_3+Mg_2Zn_3+Mg_2Zn_(11)+AlMg_2Zn→Mg_(32)(Al,Zn)_(49)+AlMg_4Zn_(11)+AlMg_2Zn等变化。Al和Zn初始阶段在AZ81镁合金表面的扩渗机理为空位扩散,Al和Zn固溶于镁合金基体表面,Zn原子首先达到最大固溶度,Mg和Zn反应生成化合物。但在390℃下扩渗,Mg和Zn的化合物不稳定,会发生分解,形成更稳定的Mg-Al-Zn化合物。Mg-Zn化合物出现后,渗层的形成机理表现为空位扩散+反应扩散+熔化分解,Mg-Zn化合物的熔化分解加速了扩散和反应扩散的进程。结论 AZ81镁合金表面固态扩渗金属Al和Zn,在同一扩渗温度下,随扩渗时间的延长,渗层的厚度、相组成、大小、形貌逐渐发生变化,扩渗合金层的主要形成机理由物理扩散转变为反应扩散。 相似文献