Papers by Author: Abdulhakim A. Almajid

Abstract: Degradation of properties due to ageing at high temperature service is a common problem which normally occurs in electricity generation power plants, refineries, petrochemical industries. This work investigates the influence of accelerated artificial ageing on the microstructural and mechanical properties of 9-12%Cr steel usually used in power plants. This steel was tested in the as-produced and aged for 2, 5 and 8 weeks at 700°C. Results showed that the microstructural features such as phases, carbides, i.e. morphology and type, sub-grains and their boundaries and misorientation angles are the dominant factors influencing the mechanical properties. Ageing led carbides to go into solution in the martensite-ferrite structure and also led to the increase of average misorientation angle as well as to the reduction of low angle grain boundaries. In addition, ageing led to the reduction in the mechanical properties and hardness when compared to the as-produced condition.

Abstract: Aluminum-Carbon composites with different weight ratio of carbon fiber were fabricated using powder metallurgy route. The mixture powders were consolidated using heat induction furnace under vacuum at temperature of 600°C and pressure 50MPa. Two different aspect ratio of carbon fiber were used in this study; namely 12 and 20. The mechanical properties of composites were evaluated by compression and hardness tests. The SEM was used to analyze the structure of the composites which showed a very good dispersion.

Abstract: Consolidated barium ferrite nanoparticles were expected to obtain better magnetic properties. Sol-gel method was used to produce the barium ferrite nanoparticles. Various calcination temperatures were set to obtain the single phase structure. XRD pattern and SEM image confirmed the nanoparticles with 48.66 nm and 70 nm, respectively. Compacted samples were sintered using microwave sintering and conventional furnace with various temperature and time. Magnetic measurement test shows that microwave sintered samples have better properties. The highest magnetic properties values for microwave sintered sample is obtained at 950°C for 60 minutes with coercivity (Hc) of 5565 Oersted, remanence (Br) of 1537 Gauss and saturation magnetization (Ms) of 37.04 emu/g.

Abstract: In the present investigation, annealed billets of commercially pure Al (1050) with coarse-grained microstructure of 0.6 mm were ECAPed through a die with an internal angle of 90o using two routes A and BC. The samples were processed up to four passes using both routes. The change in the processing route results in the change of the shear plane, and consequently the change in the produced microstructure. The microstructure study was conducted on the extrusion direction and the shear plane. The cell size, misoriention and the fraction of high angle boundaries were determined by using electron back scattered diffraction (EBSD). A study of mechanical behavior was conducted by cutting tensile and compression specimens from the ECAPed specimen in the extrusion direction to study the effect of processing route and the number of passes on the deformation characteristics. Enhanced strength was observed but with anisotropic behavior between tension and compression. Cyclic deformation under load control (HSF) was also performed and the S-N curves were established as a function of number of passes and processing route. The fractography of fractured tensile specimens was also investigated.

Abstract: Electron back scattered diffraction (EBSD) was used to document the microstructure and texture developed due to cross deformation of commercial purity 1050 aluminum alloy. The materials was first deformed in equal channel angular pressing die (ECAP) to one and two passes, via route BC and then deformed in plane strain compression (PSC) to two axial true plastic strain values of 0.5 and 1.0. The study provides a documentation of the evolution of microstructure parameters namely; cell size, misorientation angle, fraction of submicron grain size and fraction of high angle grain boundaries. These microstructure parameters were investigated on the plane normal to the loading direction in PSC (RD-TD). These microstructure parameters are compared to those achieved due to the ECAP process only. The ideal rolling texture orientations are depicted and crystal orientation maps were generated. The spatial distribution of grains having these orientations are revealed through these maps. The fraction of the main texture components for a 10o spread around the specified orientations is experimentally calculated and a quantitative idea on the evolution of microtexture is presented.

Abstract: High-temperature deformation of an artificially aged 6082-Al alloy was conducted in the present investigation. Tensile tests were carried out at temperatures of 623, 673 and 723 K at various strain rates ranging from 5x10-5 to 2x10-2 s-1. The behavior of the alloy is characterized by high stress exponent, n and high apparent activation energy, Qa that are higher than what is usually observed in Al and Al solid-solution alloys under similar experimental conditions, which implies the presence of threshold stress; this behavior results from dislocation interaction with second phase particles. The threshold stress, σo values were seen to decrease exponentially with temperature. By incorporating the threshold stress in the analysis, the true activation energy, Qt was calculated to be close to that of dislocation pipe diffusion in Al. Analysis of the experimental data of the alloy in terms of the Zener- Hollomon parameter vs. normalized effective stress, revealed a single type of deformation behavior with an n value of ~7. Measurements showed that the values of elongation percent at failure increase with strain rate and temperature.