Scope for improved properties of dissimilar joints of ferrous and non-ferrous metals

Dissimilar joints (DSJs) of ferrous and non-ferrous metals have huge technological importance in the frontiers of new designs in new machineries and improved design of conventional systems. This investigation was undertaken to improve mechanical properties of joints of two dissimilar metals: one is Ti-based and the other is Fe-based. DSJs were processed using bonding pressure from 1 to 9 MPa in step of 2 MPa at 750 °C for 60 min. Properties of the DSJs of these two metals using different mechanisms and methods were compared with the present research for verification. Experimental results from the diffusion bonding mechanism for joining the dissimilar metals validated the improvement in properties. Superior mechanical properties of dissimilar-metals joints were achieved mainly due to the third non-ferrous metallic foil, Ni of ~ 200-μm thickness, which avoided the formation of brittle Fe–Ti-based intermetallics in the diffusion zone. DSJs processed are able to achieve maximum strength of ~560 MPa along with substantial ductility of ~11.9%, which is the best ever reported in the literatures so far. Work hardening effect was detected in the DSJs when the bonding was processed at 5 MPa and above. Bulging ratio of the non-ferrous metal (Ti-based) was much higher than that of the ferrous metal (SS) of the DSJs processed. SEM analysis was carried out to know the details of reaction zone, while XRD was carried out to support the SEM results. Reasons for change in mechanical, physical, and fracture properties of the DSJs with the process parameter variations were clarified.     

表面处理对钛镍合金丝材力学性能影响研究

对经过不同表面处理的钛镍合金丝材的力学性能进行了对比分析。研究表明：与酸洗及机械抛光相比，电解抛光可有效改善钛镍丝材的力学性能，而经电镀工艺处理后的试样则易发生氢脆现象，从而显著降低材料的力学性能指标。     

High cycle fatigue and fracture behavior of 2124-T851 aluminum alloy

The high cycle fatigue properties and fracture behavior of 2124-T851 aluminum alloy were investigated roundly, including the fatigue crack growth rate, fracture toughness and fatigue S--N curve. Furthermore, the fatigue crack growth rate was analyzed by fitting the curves. And the microstructure of the alloy was studied using by optical microscopy, transmission electron microscopy and X-ray diffractometry, scanning electron microscop1/2 The results show that the fatigue strength and the fracture toughness of 2124-T851 thick plate are 243 MPa and 29.6 MPa.m at room temperature and R=0. 1, respectively. At high cycle fatigue condition, the characteristics of fatigue facture were observed obviously. And the higher the stress amplitude, the wider the space between the fatigue striations, the faster the rate of fatigue crack developing and going into the intermittent fracture area and the greater the ratio between the intermittent fracture area and the whole fracture area.     

Al2O3和Sialon陶瓷中LiTaO3第二相的断裂行为

将LiTaO3压电陶瓷颗粒分别添加到Al2O3和Sialon结构陶瓷基体中，通过对复相陶瓷试样断口形貌和裂纹扩展路径的观察，研究了Al2O3和Sialon结构陶瓷基体中LiTaO3第二相的断裂行为。研究结果表明：Al2O3和Sialon陶瓷基体的断裂均为沿晶断裂，LiTaO3压电陶瓷颗粒的断裂为穿晶断裂，在LiTaO3第二相的断口上，观察到了许多断裂台阶，这些断裂台阶是由于试样断裂时，裂纹扩展过程中遇到LiTaO3晶粒内的90°电畴发生裂纹偏转和分支引起的。     

Investigation on hydrogen-induced cracking susceptibility of HG980D steel with yield strength 900 Mpa

In this paper, the microstructure and hardness of HG980D heat-affected zone ( HAZ) at different cooling rate t8/3 were studied, the implant critical fracture stress under three diffusible hydrogen conditions were measured, and the hydrogeninduced cracking (HIC) fructograph of steel HG980D were analyzed. The experimental results show that martensite exists in HAZ of HG980 D till t8/3 ≥ 150 s, the harden quenching tendency of HG980 D is greater; The implant critical fracture stress is related to diffusible hydrogen content significantly, at low hydrogen level, high restraint stress is needed to nucleate HIC, the fructograph is mainly microvoid coalescence, but at high hydrogen level, only small restraint stress can cause HIC occurrence, the fructograph is mainly quasicleavage. It is very important to choose ultra-low hydrogen welding consumable to weld steel HG980D to prevent hydrogen-induced cracking.     

一种定向高温合金在持久过程中的组织变化及其断口分析

本文用扫描电镜研究了DZ621镍基高温合金在1100℃／60MPa持久过程中的组织变化及其断裂后的断口形貌。结果表明,合金在持久变形中γ＇相在弹性能和外加应力作用下通过扩散形成垂直于拉应力方向的筏形。筏形方向与合金的错配度和外加应力的方向有关。合金经1220℃／4h／AC＋1150℃／4h／AC＋870℃／24h／AC热处理后,具有较好的持久性能。合金断口形貌表明,裂纹源于铸造缺陷和碳化物,并在持久过程中通过各小裂纹的连接扩展,导致合金最终断裂。断口表面出现许多形态和尺寸大小不均的韧窝,显示韧性断裂特征。     

Microstructures and Properties of Laser-Glazed Plasma-Sprayed ZrO2-YO1.5/Ni-22Cr-10AI-1Y Thermal Barrier Coatings

Thermal barrier coatings (TBCs) consisting of two layers with various yttria contents (ZrO ₂- YO_1.5/Ni-22Cr-10Al- lY) were plasma sprayed, and parts of the various specimens were glazed by using a pulsed CO₂ laser. All the specimens were then subjected to furnace thermal cycling tests at 1100 °C; the effect of laser glazing on the durability and failure mechanism of the TBCs was then evaluated. From these results, two models were developed to show the failure mechanism of as- sprayed and laser- glazed TBCs: model A, which is thermal-stress dominant, and model V, which is oxidation-stress dominant. For top coats containing cubic phase, cubic and monoclinic phases, or tetragonal and a relatively larger amount of monoclinic phases, whose degradation is thermal- stress dominant, laser glazing improved the durability of TBCs by a factor of about two to six. Segmented cracks that occurred during glazing proved beneficial for accommodating thermal stress and raising the tolerance to oxidation, which resulted in a higher durability. Thermal barrier coatings with top coats containing tetragonal phase had the highest durability. Degradation of such TBCs resulted mainly from oxidation of the bond coats. For top coats with a greater amount of monoclinic phase, thermal mismatch stress occurred during cooling and detrimentally affected durability.     

明胶材料的力学性能及断口特征

研究了明胶、戊二醛（交联剂）和甘油（增塑剂）浓度对明胶材料力学性能的影响,并对明胶材料的拉钟断口进行了观察,研究表明,明胶材料的力学性能可在较大的范围内调整;随甘油浓度（即材料塑性）的变化,明胶材料的拉伸断口亦发生显著的变化。