Journal of Materials Engineering and Performance

This paper discusses the results of a series of experiments on rare earth additions to HY100. Previous work has found little or no refinement to occur with rare earth additions to this alloy. Thermal analysis has been used to provide a better understanding of this and assist in the development of a suitable grain refiner. Heats of HY100 were melted in an induction furnace and tapped into a small hand ladle. Thermal analysis cups were poured from the ladle, and the resulting cooling data recorded. Heats with no additions and 0.3 wt.% rare earth silicide were poured. Commercial software analyzed the cooling curves to determine the liquidus and solidus temperatures. A manual analysis was employed for identifying the peritectic and other reactions. Examination of the cooling curves detected the liquidus, solidus and even peritectic reactions. It was observed that the solidification changed with the rare earth silicide or engineered grain refiner additions. Additional phase reactions appeared before the solidus were not present in the baseline heat. Phase identification was done with thermodynamic calculations. The solidus, peritectic and liquidus were found. Rare earth inclusions were observed in the microstructure of the treated steel. Interestingly, macrostructure examination indicated no reduction in overall grain size. Thermodynamic predictions also indicated that the inclusions formed late during solidification. It was postulated that the additions caused a change in solidification but those occurred late enough during freezing that the resulting microstructure was not affected.

In the present work, tribocorrosion behavior of Al/Al2O3 composite strips manufactured by anodizing and accumulative roll bonding (ARB) processes was investigated. The alumina quantity was 0.48, 1.13, and 3.55 vol.% in the aluminum matrix. Tribocorrosion experiments were conducted using a ball-on-plate tribometer, where the sliding contact was fully immersed in 1 wt.% NaCl solution. The composite sample served as a working electrode and its open circuit potential (OCP) was monitored before, during, and after sliding. In order to characterize the electrochemical behavior of the surface before and after sliding electrochemical impedance spectroscopy (EIS) was used and wear was also measured. Furthermore, the influence of quantity and distribution of reinforcement particles in the matrix on OCP and EIS was evaluated. It was found that the quantity, shape, size, and dispersion of alumina particles in the aluminum matrix strongly affected the measured tribocorrosion characteristics. The results showed that inhomogeneous, lower quantity, fine, and acicular-shape alumina particles cause serious materials loss in tribocorrosion process.

TA15 and Ti2AlNb alloys were joined by diffusion welding. The influence of holding time on morphology and mechanical properties of the joint was studied under two conditions of different bonding pressure and temperature. The interface structure was analyzed by BSE and EDS. The mechanical properties of joints were tested. The results show that the typical interfacial microstructure consists of lath α-phase (TA15 alloy)/flake α phase + α-interfacial phase + α2 phase/B2-rich phase/Ti2AlNb alloy. When bonding at 920 °C and 15 MPa with increasing holding time, the interface microstructure evolves into flake α phase and distributes as a basket-weave and the interfacial coarse spherical α phase distributes as a line. α2 phase and O phase disappear gradually while the content of the B2 phase increases. The tensile strength of the joints is 870, 892 and 903 MPa, for 120, 150 and 210 min holding time, respectively, while the elongation rises as well. When bonding at 940 °C and 10 MPa with increasing holding time, the interfacial area includes more Widmanstatten structure and B2 phase. The tensile strength of joints decreases from 921 to 908 MPa, while the elongation increases from 12 to 15.5%, for holding 120 and 210 min, respectively. The tendency of plastic fracture also increases with holding time for both temperature-pressure combinations.

Khu vực chịu nhiệt (HAZ) thường là vị trí yếu nhất trong các hợp kim nhôm bị kết tủa cứng trong hàn trục trặc. Để cải thiện tính chất cơ học của HAZ bằng cách kiểm soát mức nhiệt độ, quá trình hàn trục trặc dưới nước (FSW) của hợp kim nhôm Al-Cu đã được tiến hành trong nghiên cứu này. Kết quả cho thấy độ cứng của HAZ có thể được cải thiện thông qua quá trình FSW dưới nước. Phân tích vi cấu trúc cho thấy sự cải thiện độ cứng được quy cho việc giảm mức độ gia công kết tủa và thu hẹp khu vực không có kết tủa, điều này chủ yếu do sự biến đổi của chu kỳ nhiệt trong quá trình hàn dưới tác động làm mát của nước.

Stainless steel pipes with different degrees of rouging and a Teflon®-coated rupture disc with severe corrosion were thoroughly investigated by combining multiple surface analytical techniques. The surface roughness and iron oxide layer thickness increase with increasing rouge severity, and the chromium oxide layer coexists with the iron oxide layer in samples with various degrees of rouging. Unlike the rouging observed for stainless steel pipes, the fast degradation of the rupture disc was caused by a crevice corrosion environment created by perforations in the protective Teflon coating. This failure analysis clearly shows the highly corrosive nature of ultrapure water used in the manufacture of pharmaceutical products, and demonstrates some of the unexpected corrosion mechanisms that can be encountered in these environments.

In this study, micro-dimples were prepared on a polyimide composite surface to obtain the dual benefits of polymer materials and surface texture. Micro-ultrasonic machining is employed for the first time for micro-dimple fabrication on polyimide composite surfaces. Surface textures of simple patterns were fabricated successfully with dimple depths of 150 μm, side lengths of 225-425 μm, and area ratios of 10-30%. The friction coefficient of the micro-dimple surfaces with side lengths of 325 or 425 μm could be increased by up to 100% of that of non-textured surfaces, alongside a significant enhancement of wear resistance. The results show that surface texturing of polyimide composite can be applied successfully to increase the friction coefficient and reduce wear, thereby contributing to a large output torque.

In this article, Incoloy800 and SS304 (304 stainless steel) were cladded by explosive welding. Accordingly, micro-hardness, tensile strength, shearing strength, bending properties, and SEM microstructure of cladding plate were examined in detail. The bonding interface of the plate showed a wavy morphology. Whereas, a different colorful area was observed at the wave ridge of the base layer either in optical or SEM pictures. Magnetic inspection showed that the colorful area was austenitic steel. Thus, the occurrence of the colorful areas seemed to be the result from the high deformation/cold working of the grains. EDX spectrum analysis and line scanning indicated that the diffusion through the bonding interface was not observed under the EDX and line scanning detection limitation. Micro-hardness, tensile, shearing, and bending testing results showed that the bonding strength was acceptable according to ASTM specification.

Doppler broadening measurements have been carried out to study the isochronal annealing of cold-worked commercial pure Al (99.5%) and Al-1 wt.% Mn alloys. The deduced line shape and wing parameters are investigated in the range from room temperature to 823 K and correlated with the corresponding microhardness measurements. The vacancy migration and the effect of the precipitated Al6 Mn in Al (Mn) alloys could be probed as a function of annealing temperature. Three stages of microstructures can be distinguished in both Al and Al (Mn) alloys, which are recovery, partial recrystallization, and complete recrystallization. The line shape parameter-wing parameter (S-W) map indicates the same behavior in both alloys at high temperature. However, at low temperatures, Al (Mn) shows different behavior from the linear trajectory Al alloy.