Morphology, structure and formation mechanism of silicide coating by pack cementation process

The MoSi2 coating on C 103 niobium based alloy was prepared by pack cementation method. The formative mechanism, morphology and structure of coating were investigated. The silicide coating was formed by reactive diffusion obeying parabolic rule during pack cementation process. It is found that the composite structural coating is composed of three inferior layers as follows. The main layer is composed of MoSi2, the two phases＇ transitional layer consists of NbSi2 and a few NbsSi3 and the diffuse layer is composed of NbsSi3. The dense amorphous glass layer formed on the surface at high temperature oxidation circumstance can effectively prevent the diffusion of oxygen into coating.     

Sulfidation properties of austenitic Fe-Mn and Fe-Mn-Al alloys under low sulfur vapor pressure (8 Pa) in the temperature range 873–1173 K

The sulfidation properties of austenitic Fe-Mn and Fe-Mn-Al alloys containing small amounts of carbon have been characterized with respect to the sulfidation kinetics, scale morphological development, structures, and composition of the sulfide phases. The alloys contained 21–40 wt. % Mn and 2.5–8 wt.% Al. The sulfide phase was monosulfide of manganese and iron containing the other metallic elements in solid solution. Two regimes of sulfidation categorized by slow and fast reaction rates were exhibited by all alloys when sulfidized in sulfur vapor at = 8 Pa and over the temperature range 873–1173 K. In the slow regime, a compact duplex -Mn(Fe)S/Fe(Mn)S scale evolved by a classical parabolic law associated with metal diffusion in scale. A porous microcrystalline mixed scale of the above sulfides evolved in the regime of rapid sulfidation by quasilinear kinetics associated with sulfur ingress through the porous scale.     

High Temperature Creep Deformation Mechanisms of a Hot Corrosion-Resistant Nickel-based Superalloy

Creep properties of the experimental superalloy were investigated in the temperature range 1073–1223 K and stress range 110–550 MPa. The observations of dislocation structures during different creep conditions reveal that in the high stress region, particle-shearing mechanisms including stacking fault formation and antiphase boundary creation are operative and in the low stress region, the dislocation climb mechanism is dominant. From the plot of minimum creep rate versus applied stress, a very low stress region with exponent n < 2, which is related to diffusional creep, is found. Based on the experimental results, a stress–temperature creep deformation mechanism map for the alloy is constructed. On the basis of particle hardening theories and various dislocation-creep theories, the dislocation-creep transitions in terms of internal stress are discussed and calculated threshold stresses of various creep deformation mechanisms indicates that the particle shearing is easier to operate than Orowan looping at high stresses, and general climb is easy to happen at low stresses.     

Dry friction and wear characteristics of MoSi2 against ahoy steels

The dry friction and wear characteristics of three kinds of friction couples under different loads, MoSi2/45 tempered steel, MoSi2/45 quenched steel, and MoSi2/CrWMn steel, were investigated by using a friction and wear tester. SEM and X-ray diffraction were employed to analyze the microphotograph of the worn surface and the phase of worn pieces in order to reveal the wear mechanisms of MoSi2 material. The results show that MoSi2/CrWMn steel friction pair has good dry friction and wear properties under the load of 80 N, where the friction coefficient is 0.255 and the wear rate of MoSi2 is only 14.72 mg.km-1. But under the load of 150 N, it is MoSi2/45 tempered steel friction pair that has good tribological properties,MoSi2 under low loads is brittle fracture. With the increase of load, the main wear mechanism of MoSi2 against 45 quenched steel or CrWMn steel is adhesive wear. However, the wear mechanism of MoSi2 against 45 tempered steel is changed from oxidation-fatigue wear to adhesive wear.     

汽车塑料配件注塑模具设计

通过分析两制件的使用要求和结构特点,介绍了一模成型两个不同制件的模具结构特点及模具的动作原理,研究和分析了模具结构采用斜导柱侧抽芯和斜顶相结合,进行内、外侧抽芯成型方案的合理性,给出了模具设计的详细计算过程,实现了一模成型两个不同制件的设想,得出了此模具既方便加工又节约了材料的结论.     

流动腐蚀研究的新进展

阐述了流动腐蚀的复杂性与分类.综述了电化学阻抗 谱和激光多谱勒测速等新技术在流动腐蚀研究过程中应用所形成的新的流动腐蚀实验研究方 法和测试技术，论述了流动腐蚀机理研究和数值计算法在流动腐蚀研究中的应用的一些最新 进展.最后，提出了流动腐蚀研究中的几个问题.     

斜齿轮塑件注射模的脱模机构设计

分析了塑料斜齿轮的传动优点和工艺特点，介绍了斜齿轮塑件注射成型模具的齿形型腔旋转式和斜齿轮塑件旋转式两类脱模机构设计。     

一种新型混合驱动机械压力机的研究

分析了将混合驱动凸轮连杆机构应用于机械压力机的意义,提出了一种混合驱动凸轮连杆机械式压力机的机构构型,分析了其运动原理.运用复数矢量法对该混合输入机构进行逆运动学分析,求解出伺服电机满足加工工艺要求时的实际运转情况,通过求得的伺服电机转角函数控制滑块运动.最后给出了一个设计实例,以实现滑块余弦运动规律,并在Pro/Mechanism模块中对该机构进行了运动仿真.研究表明:这种新型混合输入式机械压力机可以实现多种运动规律,从而满足多种冲压加工工艺对零件变形过程中速度变化特性的要求.     

电刷镀纳米晶镀层的组织及其强化机理

采用直流、脉冲和脉冲换向电流制备了Ni和n—SiO2／Ni电刷镀镀层，利用SEM、AFM、TEM和XRD等技术对镀层的表面形貌、显微组织和晶粒尺寸等进行了分析测量。结果表明，电刷镀层表面呈胞状组织，镀层的晶粒尺寸均在纳米量级，说明电刷镀技术是一个古老而未被认识的纳米技术；复合电刷镀过程中纳米颗粒的作用及脉冲换向电流，能进一步提高镀层的形核率及抑制晶粒的生长，从而减小纳米晶的尺寸。镀层的硬度与纳米晶的尺寸有很好的对应关系。     

高强度ZL205A合金大型铸件"白点"偏析研究

对ZL205A合金某大型铸件进行探伤检测,在底片上发现了白色点状偏析组织(以下简称“白点”偏析)。铸造工艺调整以及热处理不能使之减轻或消除。文中对ZL205A合金白点偏析进行研究,测试了偏析组织的力学性能,分析了偏析组织的微观形貌及化学成分,并探讨了其形成机理及防止措施。