Wear performance of metamorphic alloy coatings

Two Fe-Cr-B based gas atomized powders, proposed as metamorphic alloys (Arm acor M and Armacor 16), were thermally sprayed using the HVOF (High Velocit y Oxygen Fuel) process. Armacor M was also weld-surfaced by PTA (Plasma Tra nsferred Are) process. The resultant deposits were subsequently characteriz ed, using X-ray diffraction, scanning electron microscopy, and microhardnes s measurement. The wear performances of the different coatings were investi gated by two-body abrasive and pin-on-disc dry sliding wear tests. The resu lts from microstructural analysis of as-sprayed deposits reveal oxide and b oride phases such as Fe3O4 and Cr1.65Fe0.35B0.96 in a matrix for HVOF-spray ed Armacor 16 coating, and only the boride phases (Cr1.65Fe0.35B0.96 and Cr 2B) in alpha matrix for HVOF-sprayed Armacor M coating. PTA weld-surfaced A rmacor M coating contains needle-type long precipitates of large Cr2B and C r1.65Fe0.35B0.96 in alpha matrix. Wear test results show that HVOF-sprayed Armacor 16 coating exhibits the lowest wear resistance. While HVOF-sprayed and PTA weld-surfaced Armacor M coatings have the same hardness, the latter shows better abrasive and sliding wear resistance because of the size and orientation of its boride phases. More broadening in XRD patterns and hardn ess increase after wear testing suggest that the transformation from crysta lline to amorphous structure has occurred on the uppermost layer during the wear testing. However, the wear resistance of the metamorphic alloy coatin gs depends more on the density and microstructure of the coatings rather th an on the formation of amorphous surface structure. (C) 1999 Elsevier Scien ce S.A. All rights reserved.