Amir Motallebzadeh

Raman spectroscopy characterization of hypo-eutectic CoCrWC alloy tribolayers

Purpose n n n n nThis paper aims to study microstructure and high temperature tribological performance of hypo-eutectic CoCrWC hardfacing alloy (Stellite 12) deposited on steel substrate by plasma-transferred arc (PTA) welding technique. n n n n nDesign/methodology/approach n n n n nMicrostructural characterization of the deposited coating was made using electron probe microanalysis, X-ray diffraction and microhardness tester. Dry sliding wear tests were carried out with a ball-on-disc type tribometer at room and elevated temperature. Worn surfaces of the samples were examined by the EDX equipped SEM and Raman spectroscopy. n n n n nFindings n n n n nResults revealed that at room temperature and 300°C plasticity dominated wear mechanism was operative. Under oxidation dominated wear conditions (400, 500, 600 and 700°C), testing temperature plays a crucial role on the characteristics of the oxide tribolayers formed on worn surfaces. Development of Cr2O3 in the tribolayer at 600 and 700°C was beneficial in increasing wear resistance of examined coating. n n n n nOriginality/value n n n n nWhile the sliding wear performance of Stellite alloys at room temperature has been investigated in details, published studies on tribological behavior of Stellite alloys with varying temperature are scarce. Therefore, the present work was undertaken to study the wear mechanisms and the type of tribolayers formed during sliding wear of PTA welding deposited hypo-eutectic Stellite 12 coating with increasing temperature up to 700°C.

Enhanced wear resistance of Stellite 12 by Mo addition and LSM

ABSTRACT Aiming at additional improvements in the properties of Stellite 12 PTA hardfacing alloy deposited on 4140 steel substrate, the authors have adopted a dual approach. During PTA deposition Stellite 12 hardfacing powder was alloyed with 10u2005wt-% Mo, followed by laser surface melting (LSM). Addition of 10u2005wt-% Mo, led to an increase in the volume fraction of Co and W-rich complex carbides. Later on LSM executed on the PTA led to the development of unique microstructure near the surface, characterised by the segregation of hard Cr-rich carbides. The resultant layers were subjected to mechanical characterisation, at room temperature, e.g. hardness and wear resistance. It was concluded that combining both approaches i.e. addition of Mo during the hardfacing process followed by LSM of deposited layer gave additional improvements in mechanical properties owing to evolution of a unique carbide structure.

Combining benzoxazine and ketene chemistries for self-healing of high performance thermoset surfaces

A novel strategy for the synthesis and characterization of self-healable polybenzoxazine-based high performance thermoset surfaces is presented. The method involves the preparation of polymeric benzoxazine precursors from simple chemicals such as bisphenol A, formaldehyde, polyetheramines (Jeff amines) and subsequent ring opening polymerization followed by light-induced oxoketene formation. The structure and molecular weights of precursor polymers were characterized by FTIR, 1H NMR, and GPC, respectively. Successful self-healable formulations were prepared using bisbenzodioxinone (5 wt%) in the precursors, which were shown to undergo thermally activated curing by the ring opening polymerization of benzoxazines. The thermal properties of the polymers were also investigated by using DSC and TGA. Light-induced self-healing on the surface of the cured specimens was demonstrated and quantified by AFM analysis. The thermal stability differences of the cured and healed products were also investigated and compared.

Mechanical Properties of TiTaHfNbZr High-Entropy Alloy Coatings Deposited on NiTi Shape Memory Alloy Substrates

AbstractTiTaHfNbZr high-entropy alloy (HEA) thin films with thicknesses of about 750 and 1500xa0nm were deposited on NiTi substrates by RF magnetron sputtering using TiTaHfNbZr equimolar targets. The thorough experimental analysis on microstructure and mechanical properties of deposited films revealed that the TiTaHfNbZr films exhibited amorphous and cauliflower-like structure, where grain size and surface roughness increased concomitant with film thickness. More importantly, the current findings demonstrate that the TiTaHfNbZr HEA films with mechanical properties of the same order as those of the NiTi substrate constitute promising biomedical coatings effective in preventing Ni release.n