Javed Akram

Microstructures of Friction Surfaced Coatings – a TEM Study

Abstract The microstructures of dissimilar metal welds between 9Cr-1Mo (Modified) (P91) and austenitic stainless steel (AISI 304) with Ni-based alloy interlayers (Inconel 625, Inconel 600 and Inconel 800H) are reported. These interlayers were deposited by the friction surfacing method one over the other on P91 alloy, which was finally friction welded to AISI 304. In this paper, the results of microstructural evolution in the friction surfaced coated interlayers (Inconel 625, 600, 800H) are reported. For comparative purposes, the microstructures of consumable rods (Inconel 625, 600, 800H) and dissimilar metal base metals (P91 and AISI 304) were also reported. Friction surfaced coatings exhibited dynamic recrystallization. In friction surfaced coatings, the carbide particles were found to be finer and distributed uniformly throughout the matrix, compared to their rod counterparts.

Effect of Process Parameters on Friction Surfaced Coating Dimensions

Friction surfacing is a novel technology to build corrosion and wear resistant coatings and build functionally graded metallic layers. In this work, the coating dimensions as affected by process parameters and high temperature strength of consumable rods have been compared. Friction stir welding equipment, RM-1 model procured from MTI was used. Carbon steel, austenitic stainless steel and Ni-based alloy coatings were deposited. Following process parameter ranges were used: rotational speed: 1000-2000 RPM, feed rate: 50-150 mm/min and axial load: 3-12 kN. Results showed that the coating width and thickness decreased with a) increased magnitude of the process parameters used and b) increased high temperature strength of the consumable rod.

Stress Rupture Behavior of P91-AISI 304 Weld Transition Joint Developed by Friction Surfaced Additive Manufacturing Method

Weld transition joint between modified 9Cr-1Mo steel (P91) and austenitic stainless steel (AISI 304) was developed applying solid state friction surfacing method. Inconel Alloys 625, 600 and 800H were deposited as interlayers in between P91 and AISI 304 to obtain a gradual change in coefficient of thermal expansion. The post weld heat treated (750 oC/1hr/air cooling) samples were subjected to stress rupture tests at 600 and 650 oC with different stress levels. The multi-layered coated weld transition joints showed improved stress rupture lives compared to the single layer coated joints. The results were discussed in terms of the microstructural changes.