Characterisation of detonation sprayed Mo–Co–Cr–B alloy coatings

Abstract

A novel thermal spray material of Mo–Co–Cr–B with high durability in molten alloys has been developed to utilise for die casting parts and for galvanising bath parts. In the present paper, detonation gun (D gun) spray technique was used to deposit a Mo–Co–Cr–B alloy coating onto 316L stainless steel substrate, and the microstructures and mechanical properties of the coating system were studied using XRD, SEM, tensile test and Vickers microhardness. The results show that the microstructures of the coating consisted of ternary transition metal borides matrix CoMo2B2, CoMoB, as well as a little amount of binary borides, MoB and CrB. The ternary borides matrix contained both amorphous phase and nanocrystalline grains with a size of 60±35 nm. The bond strength of the coating decreases with increasing thickness of the as sprayed coatings. The anisotropy in the mechanical properties between the cross-section and plan section of the coatings is examined. Comparing the microhardness and bond strength of detonation sprayed Mo–Co–Cr–B coating with those of HVOF sprayed Mo–Co–Cr–B coating, it can be concluded that the detonation spray process has a better performance than HVOF spray process.

On corrosion behaviour of HVOF sprayed Ni3Si intermetallic powders

“…Tafel polarisation experiments were carried out using a three electrode system including platinum wire (as a counter) and a saturated calomel electrode (SCE) as a reference electrode. The tests were performed in 70%H 2 SO 4 solution using an AMETEK potentiostat (model PARSTAT 2273) at a scan rate of 1 mV s 21 . The corrosion experiments were carried out on three different locations on each specimen.…”

“…The thickness and porosity was measured to be 60¡10 mm [5][6][7][8] In the case of mechanically alloyed Ni-25Si, it has been reported that congruent melting phases like Ni 5 Si 2 (c) and Ni(Si) solid solution (a phase) can be formed during milling but non-congruent melting phases like b 1 -Ni 3 Si cannot be formed. 21 By annealing of a/c structure, single b 1 -Ni 3 Si can be formed. a/c structure also has been observed in plasma sprayed and sputtered Ni 3 Si.…”

“…[16][17][18][19] Therefore, HVOF coatings can be considered for corrosion and wear resistant applications. [20][21][22] The goal of this study was to investigate the microstructure and properties of HVOF coatings prepared from Ni 3 Si powders.…”

“…Spray parameters UnitStand off distance/cm 35 Oxygen flowrate/L min21 830 Kerosene flowrate/mL min21 260 Nozzle length/cm 20 Powder feedrate/g min21 60 Carrier gas (N 2 ) flowrate/L min21 3Secondary electron micrograph showing morphology of Ni 3 Si feedstock powders 2 a X-ray diffractograms of Ni 3 Si powders and coatings and b disappearance of superlattice Ni 3 Si peaks after spraying 3 Backscattered SEM micrograph from cross-section of Ni-Si coatings and 1?2¡0?4 vol.-% respectively. Two regions are observed in the micrograph, a grey matrix and some bright grey islands.…”

Microstructure, Mechanical Properties, Abrasive Wear, and Corrosion Behavior in Molten Zinc of Boride-Based Coatings in Situ Synthesized by an HVOF Spraying Process

“…According to the EDS analysis for the surface region of the three kinds of the coatings (as indicated by the yellow square), the elemental compositions of the three kinds of coatings after the immersion test were the same as the as-sprayed coatings (as shown in Figures 11-13); this illustrates no presence of zinc or intermetallic compounds in the coatings. The reasons for this were that, due to the excellent corrosion resistance property of ternary and binary borides for molten zinc [13][14][15][16][17][18][19][20][21][22][23], the in situ synthesized borides (e.g., CoMoB, CoMo 2 B 2 , NiMo 2 B 2 , and TiB 2 ) in this study could improve the corrosion resistance of the coatings to molten zinc. Meanwhile, the direction of lamellar microstructure (especially the boride microstructure; as shown in Figures 11-13) of the coatings was perpendicular to that of the molten zinc penetration, which also played an important role in improving the corrosion resistance of the coatings to molten zinc.…”