10138 Assessment of PTAW Tungsten Carbide-Based Overlays in an Erosive-Corrosive Environment

Available for download

Product Number: 51300-10138-SG

ISBN: 10138 2010 CP

Author: Mark Jones and Rees Llewellyn

Publication Date: 2010

Member Price: $0.00

Non Member Price: $20.00

Price: $20.00

Qty:

Two commercially available tungsten carbide-based, Ni alloy binder PTAW overlays which had both previously exhibited excellent resistance to slurry erosion (in substantially non-corrosive conditions) and abrasion were assessed in a more corrosive wear slurry environment. One overlay consisted of a 50 vol.% mixture of crushed eutectic (WC/W2C), spherical eutectic and macrocrystalline WC particles in a NiBFeSi matrix, whilst the other contained 50 vol.% macrocrystalline WC in a NiCrBSi matrix. Initial microstructural examination of the mixed carbide/NiBSi overlay, confirmed that substantial dissolution/degradation of the spherical eutectic and crushed eutectic carbides had occurred as a consequence of interaction with its matrix alloy constituent at the high temperatures encountered during arc deposition. Conversely, the macrocrystalline WC-based overlay exhibited very limited carbide dissolution or degradation.

The total erosion-corrosion (E-C) rate, as well as the separate components of erosion, corrosion and synergy, was established using a novel Slurry Pot Erosion Corrosion (SPEC) tester. The E-C rate for the macro WC/NiCrBSi overlay was approximately four times less than the E-C rate for the mixed carbide/NiBSi overlay, which performed comparatively poorly. The mixed carbide/NiBSi overlay displayed a very large synergistic value, which accounted for 90% of the total erosion-corrosion (E-C) rate, with the macro WC/NiCrBSi showing a synergy level accounting for 50% of the total E-C rate.

To establish and compare the damage mechanisms affecting both overlays, a novel technique was implemented where specific regions were examined using a Scanning Electron Microscope (SEM) before and after SPEC testing. This procedure was applied to determine any preferential attack that was occurring and to elucidate the reasons for the significantly different E-C performance of the two products.

The main reasons for the inferior performance of the mixed carbide/NiBSi overlay were found to be due to attack of the non-Cr bearing matrix and preferential removal of the W/Ni-rich boundary layer and etacarbides, formed around the eutectic carbides during deposition.

Keywords: Corrosion, erosion, erosion-corrosion, oil sands, WC overlays