Nitin Saini

Ductilizing of cast hypereutectic Al–17%Si alloy by friction stir processing:

In present research work, multi-pass friction stir processing was utilized for the as-cast Al–17%Si alloy. The multi-pass friction stir processing reproduced the aluminum (Al) matrix with a uniform distribution of the ultra-fine silicon (Si) particles. The multi-pass friction stir processing also resulted in the formation of refining cast microstructure with negligible porosity. The significant reduction in silicon particle size was measured and it reduced from 204 µm to 0.86 µm after the first pass and up to 0.30 µm after two pass friction stir processing. The frequency of fine Si particles was increased after two pass friction stir processing as compared to single pass friction stir processing. The engineering stress–strain curves revealed a significant enhancement in ductility and strength after one and two passes of friction stir processing as compared to the as-cast alloy. After one and two passes of friction stir processing, the ultimate tensile strength of as-cast alloy was enhanced by 24% and 31% and ductility was increased by 300% and 500%, respectively. The secondary electron micrograph of fracture surfaces of tensile specimens was taken before and after friction stir processing. The fractographs revealed the transformation from brittle mode to ductile dimples fracture after the multi-pass friction stir processing process.

Mechanical Properties and Wear Behavior of Zn and MoS 2 Reinforced Surface Composite Al- Si Alloys Using Friction Stir Processing

Friction stir processing (FSP) is a novel process for refinement of microstructure, improvement of material’s mechanical properties and production of surface layer composites. In present investigation, composite reinforced with using Zn/ MoS2 powder in as-cast alloy were developed at tool rotational speed of 664 rpm and tool transverse speed of 26 mm/min using FSP. Microstructural observation of MoS2/Zn reinforced composites confirmed the fine and equiaxed grains in the stir zone (SZ) and distribution of fine reinforced particles of MoS2/Zn in SZ. Moreover, agglomeration of MoS2/Zn particles were not observed. The ultimate tensile strength was measured to be 113 ± 9 and 82 ± 7 MPa for MoS2and Zn reinforced Al-Si alloy, respectively. The sliding wear was studied using pin-on-disk tribometer and it was found that FSP enhanced the wear resistance of the as-cast alloy. The MoS2 reinforced composite showed superior wear resistance than Zn reinforced composite and base material. To understand the acting wear mechanism, the field emission scanning electron microscope (FESEM) of worn out surfaces were performed.

Study on Hydrogen-Assisted Cracking in High-Strength Steels by Using the Granjon Implant Test

In present research work, the modified Granjon implant test was performed to evaluate the susceptibility of AISI 8620 and AISI 304 steels toward the hydrogen-assisted cracking. To measure the diffusible hydrogen level (HD) in deposited metal, glycerin method was employed. Shielded metal arc welding process with basic type electrode was used to deposit the metal. The hydrogen was intentionally introduced for the plate of the material AISI 304 by using an oil of grade Society of Automotive Engineers 10, which is of very low viscosity. The heat-affected zone susceptibility was quantified by finding the lower critical stress for a measured hydrogen content.