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Latest research advances on magnesium and magnesium alloys worldwide

The mechanical and microstructural properties of 316L stainless steel (SS) fabricated via Direct Laser Deposition (DLD), a laser-based additive manufacturing method, are presented and compared with those of conventionally-built counterparts. Using a Laser Engineered Net Shaping (LENS ® ) DLD system, the time interval between successive layer deposits, or inter-layer/idle time, for fabricating cylindrical specimens vertically-upward was varied by building either one or nine samples per build plate – thus increasing total assembly volume per build. Subsequently, the effect of thermal history, as well as heat treatment, on microstructural (i.e. grain size and morphology) and mechanical (i.e. tensile, compression, and microhardness) properties of DLD parts were investigated. Results indicate that the DLD 316L SS samples produced herein have a higher yield and ultimate tensile strength relative to their cast and wrought forms. Furthermore, the thermal history, microstructural evolution, and mechanical properties of DLD 316L SS are shown to be dependent on the time interval between deposits. Longer local time intervals result in higher cooling rates, leading to finer microstructures, higher/uniform strength and lower elongation to failure. In addition, porosity and less integral metallurgical bonds are found to be more prevalent in locations further upward from the build plate due to reduced laser penetration depths (e.g. previous-layer remelting decreases). Conversely, parts manufactured with shorter time intervals were found to possess a coarser microstructure, lower strength and higher elongation to failure – attributable to lower cooling rates caused by an increased bulk temperature in the part. These results may aid in future design and control of more efficient, constant-power DLD processes – especially with regard to building multiple and/or larger parts; an approach desirable for minimizing small-to-medium lot production times.

Effects of process time interval and heat treatment on the mechanical and microstructural properties of direct laser deposited 316L stainless steel

EBSD study of a hot deformed nickel-based superalloy

DAMASK – The Düsseldorf Advanced Material Simulation Kit for modeling multi-physics crystal plasticity, thermal, and damage phenomena from the single crystal up to the component scale

Hot deformation characterization of duplex low-density steel through 3D processing map development

The semisolid microstructural evolution of a severely deformed A356 aluminum alloy

The present work is devoted to investigate the correlation between the Zener–Hollomon parameter and the grain structure of the thermo-mechanically processed dual phase twinning induced plasticity (TWIP) steel utilizing the friction stir processing (FSP) technique. To this end 3 mm thick workpieces were subjected to FSP under rotational speeds of 800–2500 rpm and constant traveling speed of 50 mm/min. Additionally, isothermal hot compression tests were conducted at temperatures in the range of 800–1100 °C under the strain rates of 0.001–0.1 s −1 . Employing the flow stress data acquired from compression tests, the precise value of deformation activation energy ( Q ) was determined through Arrhenius-type constitutive model. The results indicate that increasing the rotational speed from 800 to 2500 rpm has led to Z -value variation between 1.04×10 20 and 0.03×10 20  s −1 . However, the scanning electron microscopy (SEM) characterization shows that the grain size reaches a certain minimum value at 1600 rpm. Three different models have been established to interpret the correlation between Z -value and the size of FSP-induced grains in the case of the experimental TWIP steel.

Effect of the Zener–Hollomon parameter on the microstructure evolution of dual phase TWIP steel subjected to friction stir processing

Prediction of the material flow behavior is an essential step to optimize designing any forming processes. This may be well addressed through applying a proper constitutive equation, which relates the stress and strain to the effective deformation conditions (i.e., temperature and strain rate). Accordingly in present study, the experimental true stress–true strain data from isothermal hot compression tests, in the temperature range of 800–1100 °C and strain rates of 0.001, 0.01 and 0.1 s −1 , have been employed to develop the appropriate constitutive equations for a new grade of TRIP/TWIP steel. The effects of temperature and strain rate on the deformation behavior have been represented by Zener–Hollomon parameter in an exponent type equation. Employing an Arrhenius type constitutive equation, the influence of strain has been incorporated by considering the related material constants as functions of strain. The Q -values have been in the range of 390–424 kJ/mol for different amounts of strain. Finally, the accuracy of the developed constitutive equations has been evaluated using standard statistical parameters such as correlation coefficient and average absolute relative error. The results indicate that the proposed strain-dependent constitutive equation gives an accurate and precise estimate of the flow stress in the relevant temperature range.

The prediction of hot deformation behavior in Fe–21Mn–2.5Si–1.5Al transformation-twinning induced plasticity steel

The effects of composition and intercritical heat treatment parameters on tensile strength and percentage elongation of Si–Mn TRIP steels were modeled, using a neural network with a feed forward topology and a back propagation algorithm. It was found that a committee of nets models the experimental data more accurately than a single model. The trained network was then applied to a low-carbon low-silicon steel in order to estimate the appropriate heat treatment process conditions. To explain variations in the mechanical properties, the material was subjected to a typical two-stages intercritical annealing and bainitic holding treatment. According to the results of model, tempering of material for a shorter time results in higher tensile strength and percentage elongation values. This behavior was later confirmed by microstructural studies and was attributed to both higher austenite volume fraction and higher martensite content in the samples tempered for a shorter bainitic holding.

A. Zarei-Hanzaki

Papers

Hot deformation characterization of duplex low-density steel through 3D processing map development

The semisolid microstructural evolution of a severely deformed A356 aluminum alloy

Effect of the Zener–Hollomon parameter on the microstructure evolution of dual phase TWIP steel subjected to friction stir processing

The prediction of hot deformation behavior in Fe–21Mn–2.5Si–1.5Al transformation-twinning induced plasticity steel

Ann model for prediction of the effects of composition and process parameters on tensile strength and percent elongation of Si-Mn TRIP steels