Metals2016, 6(2), 34; doi:10.3390/met6020034 - published 5 February 2016 Show/Hide Abstract
Abstract: In this study, the effects of in situ TiAl3 particles on dry sliding wear behavior of A356 aluminum alloy (added Ti) composites were investigated. The wear samples were prepared by adding different amounts of Ti (4%, 6%, and 8%) into A356 powder alloy by mechanical alloying. The mechanically alloyed powders were cold pressed at 600 MPa and sintered 530 °C for 1 h in argon atmosphere and cooled in the furnace. After the sintering process, the samples were characterized. The results show that AlTi and TiAl3 intermetallic phases were formed and their amount increased depending on the amount of Ti added into A356 powder alloy. Out of the samples sintered with different titanium amounts (1 h at 530 °C), the highest hardness value and, accordingly, the lowest wear amount, were observed in the alloy containing 8% Ti.
Metals2016, 6(2), 33; doi:10.3390/met6020033 - published 4 February 2016 Show/Hide Abstract
Abstract: Single-crystal diffuse scattering (SCDS) reveals detailed structural insights into materials. In particular, it is sensitive to two-body correlations, whereas traditional Bragg peak-based methods are sensitive to single-body correlations. This means that diffuse scattering is sensitive to ordering that persists for just a few unit cells: nanoscale order, sometimes referred to as “local structure”, which is often crucial for understanding a material and its function. Metals and alloys were early candidates for SCDS studies because of the availability of large single crystals. While great progress has been made in areas like ab initio modelling and molecular dynamics, a place remains for Monte Carlo modelling of model crystals because of its ability to model very large systems; important when correlations are relatively long (though still finite) in range. This paper briefly outlines, and gives examples of, some Monte Carlo methods appropriate for the modelling of SCDS from metallic compounds, and considers data collection as well as analysis. Even if the interest in the material is driven primarily by magnetism or transport behaviour, an understanding of the local structure can underpin such studies and give an indication of nanoscale inhomogeneity.
Metals2016, 6(2), 19; doi:10.3390/met6020019 - published 2 February 2016 Show/Hide Abstract
Abstract: This article deals with rheological and solvent extraction behavior of stainless steel 316L feedstocks using Restaurant Waste Fats and Oils (RWFO) from grease traps as binder components along with Polypropylene (PP) copolymer as a backbone binder. Optimal binder formulation and effect of solvent extraction variables on green compacts are being analyzed. Four binder formulations based on volumetric ratio/weight fraction between PP and RWFO being mixed with 60% volumetric powder loading of SS316L powder each as feedstock. The rheological analysis are based on viscosity, shear rate, temperature, activation energy, flow behavior index, and moldability index. The optimal feedstock formulation will be injected to form green compact to undergo the solvent extraction process. Solvent extraction variables are based on solvent temperature which are 40 °C, 50 °C, and 60 °C with different organic solvents of n-hexane and n-heptane. Analysis of the weight loss percentage and diffusion coefficient is done on the green compact during the solvent extraction process. Differential Scanning Calorimeter (DSC) is used to confirm the extraction of the RWFO in green compacts. It is found that all binder fractions exhibit pseudoplastic behavior or shear thinning where the viscosity decreases with increasing shear rate. After considering the factors that affect the rheological characteristic of the binder formulation, feedstock with binder formulation of 20/20 volumetric ratio between PP and RWFO rise as the optimal binder. It is found that the n-hexane solvent requires less time for extracting the RWFO at the temperature of 60 °C as proved by its diffusion coefficient.
Metals2016, 6(2), 32; doi:10.3390/met6020032 - published 2 February 2016 Show/Hide Abstract
Abstract: The high temperature deformation behavior of commercial Al-12Si-3Cu-2Ni-1Mg alloy (DM104™) which was fabricated by casting and subsequent hot extrusion was evaluated by compressive tests over the temperature range of 250–470 °C and strain rate range of 0.001–1/s. The extruded alloy had equiaxed grains, spherical Si particles and fine intermetallic phases, such as δ(Al3NiCu) and Q(Al5Cu2Mg3Si6). The true stress-true strain curves from the compressive tests exhibited steady-state flow after reaching the peak stress. A close relationship between the steady-state stress and a constitutive equation for high temperature deformation was observed. Fine equiaxed grains and a dislocation structure within the equiaxed grains were observed in the deformed specimens, suggesting the occurrence of dynamic recrystallization during high temperature deformation.
Metals2016, 6(2), 30; doi:10.3390/met6020030 - published 2 February 2016 Show/Hide Abstract
Abstract: Co-deformation of Al and Ti by accumulative roll bonding (ARB) with intermediate heat treatments is utilized to prepare multi-layered Ti/Al sheets. These sheets show a high specific strength due to the activation of various hardening mechanisms imposed during deformation, such as: hardening by grain refinement, work hardening and phase boundary hardening. The latter is even enhanced by the confinement of the layers during deformation. The evolution of the microstructure with a special focus on grain refinement and structural integrity is traced, and the correlation to the mechanical properties is shown.
Metals2016, 6(2), 31; doi:10.3390/met6020031 - published 2 February 2016 Show/Hide Abstract
Abstract: Differential speed rolling has been applied to multi-layered Ti/Al composite sheets, obtained from accumulative roll bonding with intermediate heat treatments being applied. In comparison to conventional rolling, differential speed rolling is more efficient in strengthening the composite due to the more pronounced grain refinement. Severe plastic deformation by means of rolling becomes feasible if the evolution of common rolling textures in the Ti layers is retarded. In this condition, a maximum strength level of the composites is achieved, i.e., an ultimate tensile strength of 464 MPa, while the strain to failure amounts to 6.8%. The deformation has been observed for multi-layered composites. In combination with the analysis of the microstructure, this has been correlated to the mechanical properties.