Papers by Author: Jun Bao Zhang

Abstract: In this study, 304 stainless steel particles were deposited on IF steel substrates by cold dynamic spray technology. The effect of gas temperature on bonding features and deposition critical velocity were studied and compared. The results demonstrated that the successful bonding between 304SS particle and substrate could be attributed to the adiabatic shear instability mechanism, increasing gas temperature led to enhance the particle interface bonding, deduce the deposition critical velocity, and also increase both deposition efficiency and density of coatings.

Abstract: In the present work, low carbon low alloy submicro-steel sheet has been developed successfully by severe warm-rolling (SWR) at 500 °C through a single pass. The result shows submicro-structure can be fabricated by severe rolling. The formation of the submicro-structure is attributed to the grain refinement mechanism induced by the severe plastic deformation (SPD). The refinement involves the cutting and subdividing of the original micro-crystals into ultrafine grains by dense dislocation arrays. To a certain extent, dynamic recrystallization in ferrite during SWR also seems to contribute to the formation of the submicro-structure. The thermal stability of the submicro-steel was investigated by annealing the steel at different temperatures. The investigation indicated that the submicro-steel can be subjected to annealing at 550°C without apparent grain growth. The unusually high thermal stability can be attributed to the pining effect of numerous uniformly distributed nano-precipitates in the steel. The sizes of the nano-precipitates belong to two different orders. The average diameter of the large precipitates is about 30 nm and the smaller one less than 10 nm.

Abstract: Nanostructured layers were fabricated on the surface of 0.4C-1.0Cr and 1.0C-1.5Cr low alloy steels by using an ultrasonic particulate peening (USPP) technique. The microstructures and mechanical properties of the nanocrystallized layers were characterized by means of transmission electron microscopy, and nano-indentation test. Results showed that the average grain size in the surface nanocrystallized layer of 0.4C-1.0Cr and 1.0C-1.5Cr low alloy steel was about 5nm and 10nm, respectively. The nano-indentation hardnesses of the surface nanocrystallized layer were enhanced significantly and reach upwards of 8.0 GPa and 12.5 GPa, respectively.