PSI - Issue 32

M.A. Eryomina et al. / Procedia Structural Integrity 32 (2021) 284–290 Eremina/ StructuralIntegrity Procedia 00 (2019) 000 – 000

287

4

The obtained lattice parameters for carbides agree well with the earlier reported data: for (Fe,W) 12 C the values are from 1.0934 to 1.0958 nm, for (Fe,W) 6 C the values range from 1.1060 to 1.1087 nm (ASTM 72-1988, 23-1127, 89-7205, 78-1990).

Table 2. Density and microhardness of samples and weight loss due to abrasive wear .

Density (g/cm 3 ) (±0.05)

Abrasive wear (mg ) (±0.002)

Sample

Microhardness (GPa)

Abrasive grit 28-40 µm

(%)

50-63 µm

1 12.50 2 12.39 3 10.70 4 10.42

81 9.6±2.2 85 7.4±2.1 75 7.9±2.5 73 7.3±1.1

0.0172 0.0034 0.0033 0.0026

0.0969 0.0338 0.0171 0.0106

Compacts

Coating 1

-

-

16.0 ± 2.0

-

-

Figure 2 shows SEM image of a typical microstructure of compacts for Sample 4. The grain size ranges from 100 to 600 nm for carbides. The samples are structurally homogeneous, with pores being arranged along the boundaries of the sintered powder particles. Figure 3 presents optical images of the microstructure of compacts for Samples 1-4. The pore size is seen to reduce with increasing the initial fraction of iron in the mechanically alloyed powder. 3.2. Structural-phase state of coatings The optical image and structural-phase state of the coatings are given in Fig. 4a-c for the coating obtained from the same powder as compact for Sample 1. The initial coating is rather rough. The layer remained after grinding and polishing the surface is of 70 µm in thickness (Fig. 3b). In the phase composi tion of the coating, tungsten and (Fe,W) 6 C carbide predominate, with also a small amount of (Fe,W) 12 C carbide. The reflexes of iron refer to the substrate material. During sintering, layers of lower-melting point iron of the substrate are mixed with the coating material, resulting in passing of iron partially into the coating composition. The noticeably lower fraction of carbides in the coating as compared to the compacts is apparently due to partial laser damage of carbon. In this case, there are no oxide phases in the composition of the coatings. Thus, both annealing of compacts at 900°C and selective laser sintering of the mechanically synthesized powder provide composites based on η -carbides (Fe,W) 6 C and (Fe,W) 12 C. 3.3. Density and microhardness of samples The absolute and relative values of density of the obtained compacts decrease with increasing the bcc Fe proportion. The absolute value of density reduces because of lower density of iron (Table 2). The lower relative density indicates a higher porosity of the compacts. The microhardness also decreases with increasing the proportion of iron because of its lower hardness as compared to tungsten and tungsten carbides. The microhardness of η -carbides of the Fe-W-C system ranges from 12 to 17 GPa. Lower values of microhardness of the obtained compacts are due to their porosity (see Fig. 2 and Table 2). Compared to compacts, the coating has microhardness of 16 GPa, despite a significant proportion of tungsten in its composition. 3.4. Wear resistance of samples Table 2 provides the values for the mass loss of compacts after abrasive wear tests. In spite of lower density and microhardness of samples in a series of samples 1-4, their abrasive wear resistance increases, on the contrary. The lowest abrasive wear resistance is observed for compact of Sample 1 containing 17 wt% of tungsten. The presence