Microstructure evolution and thermal stability of an Fe-based amorphous alloy powder and thermally sprayed coatings

作者：Chokethawai K; McCartney D G^*; Shipway P H

来源：Journal of Alloys and Compounds, 2009, 480(2): 351-359.

DOI：10.1016/j.jallcom.2009.02.035

• Coating materials
• Thermal spraying
• Microstructure
• Amorphous materials
• Thermal analysis

High velocity oxy-fuel (HVOF) thermal spraying has been used to produce coatings of an Fe-18.9%Cr-16.1%B-4.0%C-2.8%Si-2.4%Mo-1.9%Mn-1.7%W (in at.%) alloy from a commercially available powder (Nanosteel SHS7170). X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) were employed to investigate the powder, as-sprayed coatings and annealed coatings which had been heated to temperatures in the range of 550-925 degrees C for times ranging from 60 to 3900 min. Microhardness changes of the coatings were also measured as a function of annealing time and temperature. The powder was found to comprise amorphous and crystalline particles; the former had a maximum diameter of around 22 mu m. The coating was composed of splat like regions, arising from rapid solidification of fully molten powder, and near-spherical regions from partially melted powder which had a largely retained its microstructure. The amorphous fraction of the coating was around 50% compared with 18% for the powder. The enthalpies and activation energies for crystallization of the amorphous phase were determined. Crystallization occurred in a two stage process leading to the formation of alpha-Fe (bcc), Fe(1.1)Cr(0.9)B(0.9) and M(23)C(6) phases. DSC measurements showed that the first stage occurred at 650 degrees C. Annealing the coating gave a hardening response which depended on temperature and time. The as-sprayed coating had a hardness of 9.2 GPa and peak hardnesses of 12.5 and 11.8 GPa were obtained at 650 and 750 degrees C, respectively. With longer annealing times hardness decreased rapidly from the peak.

• 出版日期2009-7-8