Mohammad Jahazi

Bio: Mohammad Jahazi is an academic researcher from École de technologie supérieure. The author has contributed to research in topics: Welding & Microstructure. The author has an hindex of 41, co-authored 270 publications receiving 6459 citations. Previous affiliations of Mohammad Jahazi include IAR Systems & École Normale Supérieure.

Microstructure and tensile properties of friction stir welded AZ31B magnesium alloy

Abstract: The microstructural change in AZ31B-H24 magnesium (Mg) alloy after friction stir welding (FSW) was examined. The effects of tool rotational speed and welding speed on the microstructure and tensile properties were evaluated. The grain size was observed to increase after FSW, resulting in a drop of microhardness across the welded region from about 70 HV in the base metal to about 50 HV at the center of the stir zone. The obtained Hall–Petch type relationship showed a strong grain size dependence of the hardness. The aspect ratio and fractal dimension of the grains decreased towards the center of the stir zone. The welding speed had a significant effect on the microstructure, with larger grains at a lower welding speed. The yield strength and ultimate tensile strength increased with increasing welding speed due to a lower heat input. A lower rotational speed of 500 rpm led to higher yield strength than a higher rotational speed of 1000 rpm. The friction stir welded joints were observed to fail mostly at the boundary between the weld nugget and thermomechanically affected zone at the advancing side. Fracture surfaces showed a mixture of cleavage-like and dimple-like characteristics.

Linear friction welding of Ti-6Al-4V: Processing, microstructure, and mechanical-property inter-relationships

Abstract: The linear friction welding behavior of Ti-6Al-4V was investigated using varying processing conditions of frequency (15 to 70 Hz), amplitude (1 to 3 mm), pressure (50 to 90 MPa), and axial shortening (1 to 2 mm). Examination of linear friction welded Ti-6Al-4V using microscopic techniques indicated that the process requires certain critical conditions at the interface and its adjacent region to be reached for producing joints without structural defects along the weld centerline, such as voids or oxide inclusions. Characterization of the weldments included analysis of the microstructural features of the weld and thermomechanically affected zones (TMAZs) in relation to the parent material. It was observed that in the weld region, exposure to supertransus temperatures (>995 °C) combined with hot-deformation working and rapid cooling after joining produced recrystallization of the beta grain structure that had a Widmanstatten alpha-beta transformation microstructure. In the TMAZ, the bimodal microstructure of the parent material was deformed and the presence of elongated alpha grains with broken beta-phase particles was established. Through examination of the mechanical properties, using microhardness and tensile testing, the integrity of the joints was determined in order to assess the impact of the various processing parameters and to define the optimum welding conditions.

Hot working behavior of near-α alloy IMI834

Abstract: In this work, the flow stress behavior of near-α alloy IMI834 was investigated by compression testing under isothermal hot working conditions of varying temperature (between 950 °C and 1125 °C) and strain rates (between 0.001 s −1 and 1 s −1 ) up to a true strain of 0.8. The flow stress behavior revealed greater flow softening in the α–β region as compared to the β region together with the occurrence of a yield point phenomenon at high strain rates and temperatures above the β-transus. Through examination of the influence of temperature and strain rate on the hot working behavior, it was determined that the experimental flow stress observations could be effectively related to the processing parameters using an Arrhenius-type hyperbolic-sine relationship. Constitutive equations that describe the flow stress as a function of the strain rate and temperature are proposed for isothermal hot working of IMI834 in the β and α–β phase regions.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Metal Additive Manufacturing: A Review of Mechanical Properties

Abstract: This article reviews published data on the mechanical properties of additively manufactured metallic materials. The additive manufacturing techniques utilized to generate samples covered in this review include powder bed fusion (e.g., EBM, SLM, DMLS) and directed energy deposition (e.g., LENS, EBF3). Although only a limited number of metallic alloy systems are currently available for additive manufacturing (e.g., Ti-6Al-4V, TiAl, stainless steel, Inconel 625/718, and Al-Si-10Mg), the bulk of the published mechanical properties information has been generated on Ti-6Al-4V. However, summary tables for published mechanical properties and/or key figures are included for each of the alloys listed above, grouped by the additive technique used to generate the data. Published values for mechanical properties obtained from hardness, tension/compression, fracture toughness, fatigue crack growth, and high cycle fatigue are included for as-built, heat-treated, and/or HIP conditions, when available. The effects of test...