Materials Science Forum Vol. 1016

Abstract: The temperature-dependent mechanical stability of retained austenite in medium-Mn transformation induced plasticity 0.17C-3.3Mn-1.6Al-1.7Al-0.22Si-0.23Mo thermomechanically processed steel was investigated using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) methods. Specimens were deformed up to rupture in static tensile tests in a temperature range 20–200°C. It was found that deformation temperature affects significantly the intensity of TRIP effect. In case of specimens deformed at temperatures higher than 60°C, a gradual temperature-related decrease in the stability of γ phase was noted. It indicates a progressive decrease of the significance of the TRIP effect and at the same time the growing importance of the thermally activated processes affecting a thermal stability of retained austenite.

Abstract: The influence of grain refinement by high pressure torsion (HPT) on microstructure of the Mg-1%Ca alloy was investigated by scanning and transmission electron microscopy. To The microhardness measurements and tensile tests of small samples were used to determine the mechanical properties of UFG samples. It was found that a uniform structure with an average grain size of 210 nm processed by HPT lead to high microhardness equal to 100 HV. Investigations of thermal stability demonstrated that additional heat treatment of the UFG samples at 250 oC provides good combination of high strength of 245 MPa and ductility of 4%.

Abstract: The effects of welding conditions such as the electrode type and welding current were investigated on the microstructure and joint strength of the resistance weld of A5052 and GA590. The reaction layer formed at the joint interface was inferred to consist of Fe-Al based intermetallic compounds (IMCs) which are FeAl, FeAl₂, Fe₂Al₅ and FeAl₃ by quantitative analysis. Although the thickness of the IMCs layer decreased from the center of the nugget towards the edge of it. When the DR type electrode was used, the cross tensile force became higher than those of the joints formed with the R type one. This is because the thickness of the reaction layer formed at the nugget end of A5052 was thin in the case of the DR type electrode. Also, it was found that cross tensile force increases when the thickness of the reaction layer is thin by multiple regression analysis.

Abstract: Severely-deformed high-strength brasses were investigated by leveraging high-pressure torsion (HPT) processing in order to obtain more enhanced mechanical properties of copper alloys. Pure copper, binary Cu-Zn solid-solution alloys and high-strength brasses including aluminum and manganese additions were selected for experiments. For comparison of these materials, zinc equivalent parameter was used. These materials were subjected to the HPT processing, followed by hardness tests and tensile tests. The maximal hardness value of the nanostructured high-strength brass with β phase matrix was reached 420 HV. The HPT processed high-strength brass with β phase matrix showed significant increase in the yield stress and tensile strength with sacrificing ductility. The tensile specimen of the high-strength brass with β phase matrix was fractured before initiation of necking. It was found that utilizing β phase matrix is also beneficial for controlling enhanced strength of high-strength copper alloys for not only casting process but also severe plastic deformation.

Abstract: Thus far, our research group has conducted a basic investigation for the development of an artificial ligament, which was performed by utilizing a biogenic secretion that was derived from the Achilles tendon in mice; this was achieved using the film model method. In this study, an attempt has been made to derive a biogenic secretion from the Achilles tendon (tendon gel) and the medial collateral ligament (ligament gel) in rabbits. Subsequently, a discussion was carried out on the possibility of forming a ligament-like structure that was based on the structural, mechanical, and spectroscopic investigations. The tendon gel was successfully formed from a parent tendon that was preserved in vivo for 3, 5, 10, and 15 d. Further, an aligned collagen fiber emerged in the tendon gel, which was subjected to tension on every preservation date. Further, the mechanical behavior of the tendon gel specimens was classified in two groups. The values of the Young's modulus of the specimens preserved for 10 and 15 d were higher than those of the specimens preserved for 3 and 5 d. Within the range of this experimental condition, the aligned collagen fiber structure was formed by applying a tension of approximately greater than 0.05 N. Conversely, only a 10-d preservation period yielded a sufficient amount of ligament gel for the experiment. Notably, the volume of ligament gel was less than that of the tendon gel. In the ligament gel specimen without the synovial membrane, the collagen fiber structure was formed by applying a tension, which was similar to that experienced by the tendon gel specimen. However, the cross-linking and growth of collagen fibers in the ligament gel samples were insignificant as compared with those of the tendon gel samples.

Abstract: Samples of TiAl-based matrix in-situ composite with the chemical composition Ti-46.4Al-5.1Nb-1C-0.2B (at.%) reinforced with a low volume fraction of primary Ti₂AlC particles were prepared by vacuum induction melting in graphite crucibles and centrifugal casting into graphite moulds. The hot isostatic pressing (HIP) of the as-cast samples and subsequent heat treatments leads to the formation of equiaxed grains with fully lamellar α₂(Ti₃Al) + γ (TiAl) microstructure and uniformly distributed Ti₂AlC and TiB particles. The minimum creep rates of the in-situ composite are significantly lower compared to those measured for the counterpart low carbon benchmark alloy with the chemical composition Ti-47Al-5.2Nb-0.2C-0.2B (at.%) at temperatures ranging from 800 to 900 °C and applied stress of 200 MPa. The studied in-situ composite shows also significantly improved creep resistance compared to that of some TiAl-based alloys with fully lamellar, convoluted and pseudo-duplex microstructures at a temperature of 800 °C and applied stress of 200 MPa.

Abstract: Cold spraying is being developed as effective and promising additive manufacturing process. However, how to create a deposit by cold spraying with comparable properties to bulk material is still challenge. It is well known that post-spray annealing is an effective process to enhance the deposit properties. In this paper, copper deposits are cold-sprayed at three different sets of spray conditions corresponding to three mean particle velocities of 578, 745, and 807 m/s. The tensile strength, thermal conductivity and electrical conductivity are measured at three different directions to clarify the anisotropy of deposit properties, which are parallel to gun moving direction and other two perpendicular directions. Furthermore, the influence of post-spray annealing on the anisotropy effect is also investigated by examining the effect of spray conditions and annealing conditions on the deposit properties at three different directions. The results clearly demonstrate the anisotropy of as-deposited Cu. Although it can be found that post-spray annealing significantly improves the properties of the as-sprayed deposits and reduces anisotropy of Cu deposit properties, the microstructure of the as-sprayed initial Cu deposit presents a significant effect on final annealed deposit. Therefore, an optimized cold-sprayed deposit will benefit manufacturing of a deposit with comparable properties with bulk by cold-spraying combined with post-spray annealing.

Abstract: In the framework of Accident tolerant fuel (ATF) program, several types of claddings and pellets with enhanced accident tolerance have been developed for light water reactors. Oxide dispersion strengthened (ODS) FeCrAl alloys have been considered as a promising candidate for cladding materials due to their good mechanical strength, excellent structural stability and chemical durability at high temperature. The out-of-pile performance of 14Cr ODS-FeCrAl cladding tube fabricated by cold-rolling, such as microstructure, thermophysical property, mechanical property, and corrosion resistance, has been examined and discussed. The results confirm that iron-based ODS alloy is one of the promising candidates to be used as ATF cladding. It could also aid in the supplement of property database of ODS-FeCrAl for future use in nuclear cladding and structural applications in next generation nuclear systems.

Abstract: Coarse form-stable phase change materials (FS-PCMs) can tailor the properties of pure PCMs. This is often attained by the presence of high-melting, high-thermal conductivity metallic phase which enhances the thermal energy storage/release. The evaluation of the thermal response of these composite materials in unsteady conditions, is not an easy task, and simplifications introduced to deal with them must be carefully considered. A set of FS-PCMs of prismatic geometry with polymeric wax as PCM and an Al foam with various pore sizes, modelled as BCC lattice has been considered in this paper. The thermal response under a set of boundary conditions with constant heat flux at the bottom surface, all other being adiabatic, was investigated both by direct simulations approach modelling the two phases and the ‘1-temperature model’, which considers the material as homogeneous and characterized by a proper set of effective properties. The ‘1-temperature model’ is able to closely reproduce the whole the local thermal history only within certain validity ranges, even if it can well reproduce the ‘average’ energy storage due to the transformation of the PCM phase.

Abstract: Stress corrosion cracking (SCC) is one of serious aging degradation problems for the Alloy 600 components of pressurized water reactors (PWRs). In order to prevent SCC, various methods such as water jet peening (WJP), laser peening (LP), surface polishing have been used to introduce compressive stresses at the surfaces of the PWR components. However, it has been reported that such compressive residual stress introduced by these methods might be relaxed during the practical operation, because of high temperature environment. In this study, the hardness reduction behavior of the Alloy 600 processed by LP, Buff and WJP in the thermal aging process has been investigated to estimate the stability of the residual stress improving effect by each method, based on the fact that there is a correlation between the compressive residual stress relaxation and the decrease of hardness. The behavior of the residual stress relaxation in the processed materials in the high temperature environment has been discussed with kinetic analysis.