Materials Science Forum Vol. 879

Abstract: Effect of B addition on the microstructure and mechanical properties of AZ84 Mg alloy was investigated in this study. Through calculation of phase equilibria of AZ84 Mg alloy, carried out by using FactSage® and FTLite database, solution treatment temperature was decided as temperature of 330^oC, where supersaturated solid solution can be obtained. Solid solution treatment of AZ84 Mg alloy was successfully conducted at 330^oC and supersaturated microstructure with all almost all phases resolved into matrix was obtained. After solution treatment, hot rolling was successfully conducted by reduction of 60%. Compression and tension tests were carried out at room temperature on the samples in as-cast, solution treated, hot-rolled and subsequently recrystallized states. After solid solution treatment, each alloy was soaked at temperatures of 180 and 200^oC for time intervals from 1 min to 48 hrs and hardness of each condition was measured by micro-Vickers method. Peak aging conditions were deduced as at the temperature of 200 ^oC for 10 hrs for ZA84 Mg alloy. By addition of boron, aging kinetics was expedited and strength was enhanced.

Abstract: Milling and drilling of titanium alloys represent a key technology for the aircraft manufacturers. The balancing act between production costs and tool costs leads to the need of tests and an optimized setup of the whole process. A Styrian consortium with experts in materials, tools and machining has been formed to extend the tool life in machining of titanium alloys. A series of tests is set up to evaluate the roughing and finishing operations. For finishing operations ultrasonic assisted milling is introduced and compared with conventional milling. Force measurement and optical wear detection are used for tool characterization.

Abstract: Complicating factors that have stymied understanding of uranium-niobium’s aging response are briefly reviewed, including (1) niobium inhomogeneity, (2) machining damage effects on tensile properties, (3) early-time transients of ductility increase, and (4) the variety of phase transformations. A simple Logistic-Arrhenius model was applied to predict yield and ultimate tensile strengths and tensile elongation of U-4Nb as a function of thermal age. Fits to each model yielded an apparent activation energy that was compared with phase transformation mechanisms.

Abstract: Casting of an Mg alloy clad strip was attempted with a twin roll caster equipped with a scraper in an oxidizing atmosphere. The base strip was AM60 and the overlay strip was AZ121. The AM60 strip was cast with a roll, and the upper side of the strip was scribed by the scraper. The molten AZ121 was poured on the scribed AM60 strip. The scribed surface of AM60 contacted the molten metal of AZ121 without exposure to the atmosphere. Therefore, the scribed surface was not oxidized. Most of the AZ121 strip was solidified by the other roll. The casting speed was 30 m/min. The roll load was 0.05 kN/mm. The roll speed was very high and the roll load was very small. However, the strips were bonded, and they did not peel with bending until breaking. The interface between the two strips was clear. When AM60 was on the outer side, the results of the V-bending test and the Erichsen test were better. These results mean that the ductility of AZ121 was improved by cladding with AM60.

Abstract: The effect of alloying element (such as Cr, Zr, and Ir) addition on the high-temperature creep deformation behavior of C40/C11_b lamellar-structured (Mo_0.85Nb_0.15)Si₂ silicide crystals was examined. The results indicated that these additions all lead to a decrease in the steady-state creep strain rate (SSCR) when the applied stress is parallel to the lamellar interface. To clarify the origin of this, the dependence of the creep deformation behavior on the microstructure was determined in detail. As a result, it was found that the C40 phase acts as a strengthening phase during the deformation of the C40/C11_b duplex-phase crystals. The variant-1-type C11_b phase grains, whose loading orientation is parallel to [001], also acts as an effective strengthening component. The decrease in SSCR by Cr or Zr addition is attributed to the increase in volume fraction of those C40 phase and C11_b-V1 grains. The refinement of microstructure by Ir addition was also found to result in a modest decrease in the SSCR.

Abstract: Open cell aluminum foams are a promising multi-functional material that has potential application in a variety of engineering fields, but their too low mechanical properties may restrict their applications in some load bearing conditions. To overcome this shortcoming, enhancement methods have been widely investigated in recent years including surface enhancement technologies. In the present study, an electrodeposition process was utilized to coat an amorphous Ni-P coating on the cell strut surface of open cell aluminum foams. The results show that the coated film exhibits typical amorphous feature and is thermally stable. The average nanohardness and Young’s modulus are 7.0GPa and 118.1GPa, respectively, in which the Young’s modulus is even 1.6 times higher than that of aluminum (70GPa). It is because the high strength film that leads to significantly enhancement of the foams. The compression strength of the foam was increased from about 0.2MPa to 11.9MPa when the film thickness was around 65μm. These results demonstrate that the surface coating does be an effective way to improve the mechanical properties of open cell aluminum foams.

Abstract: Al-based amorphous materials are believed to be a promising light weight and high strength material, but the application has not yet been realized due to difficulties in fabricating bulk materials resulted from their quite weak glass forming ability. In order to overcome this difficulty, a solid state route was studied to fabricate bulk Al-based metallic glass. An amorphous Al₇₂Ni₈Ti₈Zr₆Nb₃Y₃ powder was first fabricated by mechanical alloying, and then the microstructure, glass-forming ability and crystallization behavior were characterized. The powder shows a wide supercooled liquid region (81K), and high activation energy for crystallization (312.6kJ/mol). By this powder, a bulk material was fabricated through high pressure (2GPa) sintering (673K and 723K). The microhardness of bulk sample is as high as 1215Hv, providing a solid basis for fabricating bulk materials and applications.

Abstract: To guarantee the reliability and safe operation of large-scale metallic structures exposed to cryogenic temperatures for extended periods, it is important to evaluate structural properties of the base metal as well as the welded zone in order to prevent damages that could occur. Spatially-resolved high-energy synchrotron diffraction, pulsed neutron diffraction and small-angle neutron scattering have been used to study short, intermediate and mesoscopic range order in cryogenic 9Ni steel as well as the structural changes induced by the welding. Pristine 9Ni steel appears to be a metastable Fe-Ni alloy with main bcc martensitic phase and a minority fcc austenitic phase. Welding of 9Ni steel using SMAW technique has revealed a fast intergranular nickel diffusion at high temperatures during welding originated from high nickel content in the SMAW welding alloy.

Abstract: Magnesium alloy has a wide range of application prospects in the automobile and electronic industries. However, peeling of the coating material may occur under harsh environments such as high and low temperatures and high humidity with the conventional coating techniques. The authors have proposed a lining process of metals with thin aluminium foils using shot peening. In this method, the foil can be bonded to the workpiece surface bringing about large plastic deformation. The pressure generated by the hit of many shots is utilized for the bonding. In the present study, to improve the surface characteristics of magnesium alloy, the formation of an Fe-Al intermetallic compound film on magnesium alloy by compound treatment combining shot lining method and heat treatment was mainly investigated. Shot peening was performed with a centrifugal-type machine using cast steel ball. The lined sheet is aluminum foil with pure iron powders, and the workpiece was the commercial magnesium alloys. The lined workpieces are heat treated by laser in air. The Vickers hardness test was performed with a microhardness tester. It was confirmed that the present method could be used for the formation of functional films on the magnesium alloy.

Abstract: The behavior of environment-assisted cracking (EAC) for super-elastic TiNi alloy was investigated as functions of solution pH and electrochemical potential. The specimen was immersed in sulfate solutions at various pHs, and subjected to a potentiostatic slow strain rate tensile test. As a result, the EAC map for the TiNi alloy as functions of the solution pH and the applied potential was successfully produced, and it was revealed that larger EAC susceptibility was obtained in the region of lower potential and lower pH. The tendency was quite typical for hydrogen embrittlement, but not similar to that of TiAl. The EAC susceptibility was classified by cathodic charge density, irrespective to pH nor potential: The charge density larger than 0.025 MC^.m^-2 induced a maximum EAC susceptibility.