Muneer Baig

Mechanical properties, microstructure and toughness assessment of a X70 pipeline steel

Abstract This study was performed to fully characterize the microstructure, texture and mechanical properties of API X70 steel in terms of tensile and compressive responses and toughness. The toughness was studied using a compact-tension specimen that was machined in three directions. The variations in the toughness values along three orientations were studied and revealed almost similar high values of 124 ± 4 MPa√m. Compression experiments were performed over a wide range of strain-rates. A compression split Hopkinson pressure bar (SPHB) was used for performing dynamic experiments. API X70 exhibited positive strain-rate sensitivity of 0.01. Electron back scattered diffraction and optical microscopy revealed a grain size of 2.4 µm with an average misorientation angle of 30°. Texture study revealed high orientation density values around the γ-fiber. The results suggest that the present steel exhibits high strength, elongation and toughness.

Microstructure characterization and corrosion resistance properties of Pb-Sb alloys for lead acid battery spine produced by different casting methods

The aim of this study is to find out the microstructure, hardness, and corrosion resistance of Pb-5%Sb spine alloy. The alloy has been produced by high pressure die casting (HPDC), medium pressure die casting (AS) and low pressure die casting (GS) methods, respectively. The microstructure was characterized by using optical microscopy and scanning electron microscopy (SEM). The hardness was also reported. The corrosion resistance of the spines in 0.5M H2SO4 solution has been analyzed by measuring the weight loss, impedance spectroscopy and the potentiodynamic polarization techniques. It has been found that the spine produced by HPDC has defect-free fine grain structure resulting improvement in hardness and excellent corrosion resistance.

The effect compatibilizer on mechanical properties of short carbon fiber reinforced polypropylene composites

Short carbon fiber (SCF) reinforced Polypropylene (PP) composites were fabricated using twin-screw extruder followed by injection molding process. The SCF used is of 7-9 µm diameter and 90µm length (SCF90). SCF were loaded at two different percentages, 15%wt and 35%wt. Different %wt loading of compatibilizer (Maleic Anhydride grafted Polypropylene (MAPP)) ranging from 0 to 4 %wt were used. For 15 wt% loading, higher %wt of MAPP increases the ductility but the strength and modulus remain at the same level as without MAPP. Optimal %wt was found to be at 2%wt of MAPP. For 35 %wt loading, no change on the ductility observed but slight drop in the modulus and strength at 4 %wt loading.

Evaluation of residual stresses present in spirally welded API grade pipeline steel using the hole drilling method

Abstract The mechanical and microstructural characterization of a material prior to its installation for the desired service is imperative to avoid material or structural failures. Of the several mechanical properties affecting the performance of a material, the residual stresses (RS) constitute an integral part of the material property and arise mostly during the manufacturing processes. They can be either beneficial or detrimental to material performance depending on their nature and magnitude. In this study, the microhardness, the tensile and the nature and magnitude of RS present in the weldment zones, base material (BM), heat affected zone (HAZ) and weld nugget (WN) of spiral welded (SWP) API grade line pipe steel, were determined. The microhardness and tensile responses were observed to have significant demarcation depending on the location where examined. The RS were measured using a nondestructive X-ray diffraction (XRD) and a semidestructive hole drilling (HD) technique. The results from both measurement techniques are found to be in good agreement. The BM microstructure consisted of ferrite and pearlite phases with ferrite constituting the dominant phase. The WN comprised of multi-passes, which consisted of root (hot) and the reinforcing (filling) pass. The microstructure of the reinforcing passes can be described as columnar grains/structure.

Quasi and Dynamic Compression of ECAP Processed AA 6082

AA 6082 in as received T651 condition was solution treated and immediately processed via equal channel angular pressing (ECAP) to one and two passes and then naturally aged to 100 days. The processed samples were subjected to quasi and dynamic compression testing using regular universal testing machine and split Hopkinson pressure bar (SHPB), respectively. The testing was conducted at a wide range of strain rates and temperatures and the constitutive Johnson model constants were identified. The effect of cryo temperature versus room temperature during dynamic compression was, also, evaluated in terms of the evolution of microstructure and stress — strain response.

Effect of different compaction and sintering conditions on the thermo-mechanical properties of bulk aluminium produced using mechanical alloying

Abstract In the investigation reported here, coarse-grained Al powder (85 μm) was subjected to ball milling for 4 h in an attritor at room temperature under argon atmosphere. The bulk aluminium samples consisting of ultrafine and nanocrystalline grains were prepared from ball-milled powders using a high frequency induction sintering machine. The bulk samples were investigated for the enhancement in mechanical properties using uniaxial compression experiments to large strains. Vickers micro hardness measurements were made along the diametral line of the bulk samples. A comparative study on the effect of mechanical properties of bulk samples obtained through different processing conditions was addressed and an optimum processing condition is established. The variation in strain-rate sensitivity with different processing conditions of the bulk samples was also investigated.

Effect of Consolidation and Sintering Parameters on the Mechanical Responses of Nanocrystalline Al-Fe Alloy Processed by Mechanical Alloying

In this investigation, bulk ultra-fine grained and nanocrystalline Al-2 wt.% Fe alloy was produced by mechanical alloying (MA). The powder was mechanically milled in an attritor for 3 hours and yielded an average crystal size of ~63 nm. The consolidation and sintering was performed using a high frequency induction sintering (HFIS) machine at a constant pressure of 50 MPa. The prepared bulk samples were subjected to uniaxial compressive loading over wide range of strain rates for large deformation. To evaluate the effect of sintering conditions and testing temperature on the strain rate sensitivity, strain rate jump experiments were performed at high temperature. The strain rate sensitivity of the processed alloy increased with an increase in temperature. The density of the bulk samples were found to be between 95 to 97%. The average Vickers micro hardness was found to be 132 Hv0.1.

The fracture strength of cryomilled 99.7 Al nanopowders consolidated by high frequency induction sintering

Mechanical Attrition of metallic powders induces severe plastic deformation and consequently reduces the average grain size. Powders of 99.7 Al (45μm particle size), cryomilled for 7 hrs having a crystal size of ~ 20 nm, were consolidated by high frequency induction sintering under a constant pressure of 50 MPa and at two temperatures of 500 and 550 °C for two sintering dwell times of 1 and 3 minutes at a constant heating rate of 400 °C/min. The bright field TEM image and X-ray line broadening technique, for the cryomilled powders, were used to measure-the crystallite size. Simple compression at an initial strain rate of 10−4 s−1 was conducted at room temperature, 373 and 473 K, and the yield strength was documented and correlated with the sintering parameters. The as-received 99.7 Al powders-consolidated using one of the sintering parameters was used as a reference material to compare the mechanical properties. Hardness, density and crystal size of the consolidated sample, that gave the highest yield and fracture strength, were measured.

Thermo-mechanical large deformation responses of an aluminum alloy processed by Equal Channel Angular Pressing (ECAP)

O of the major roadblocks to large enhancements in the thermoelectric figures of merit (ZT) of leading candidate thermoelectric materials such as the Bi2Te3, PbTe, CoSb3 and half-Heusler (HH) based systems remains the difficulty in making meaningful simultaneous improvements in both the electrical conductivity (σ) and thermopower (S) of these materials through doping and/or substitutional chemistry. In conventional semiconductors, both materials parameters (S and σ) are fundamentally coupled adversely through the concentration, n, of charge carriers. Therefore, the maximization of one parameter by tuning n via doping and/or substitution inevitably results in the minimization of the other. Here, we show that by coherently embedding sub-ten nanometer scale inclusions within a semiconducting HH matrix, large enhancements of S and the mobility (μ) can be achieved simultaneously in both n-type and p-type nanocomposites. The enhancement in thermopower originates from large reductions in the effective carrier density (n) coupled with an increase in the carrier effective mass (m*). The surprising enhancement in the mobility is attributed to an increase in the mean-free time (τ) between scattering events (phonon-electron, ionized-impurity, and electron – electron). Using X-ray powder diffraction, electron microscopy, and electronic transports data, we will discussed the mechanism of phase formation at the sub-ten nanometer scale, in bulk HH matrix and the mechanism by which the embedded nanostructures regulate electronic charge transport within the semiconducting HH matrix to achieve unprecedented combinations of physical properties such as, large enhancements in μ, S and σ simultaneously with drastic decrease in thermal conductivity (κ) at high temperatures.