**3. Results and discussion**

### **3.1. Characterization of porous skeletons**

The combined effects of tungsten carbide content and powder processing route on the relative density and shrinkage of the porous skeleton are shown in Figure 4 and 5.

**Figure 4.** Relative densities of green compacts and pre-sintered porous skeletons as a function of tungsten carbide WC content

Figure 5 shows the effect of WC content on compressibility and shrinkage of high speed steel powders. It is evident that green density of compact decreases with increasing WC content. This attributes to hard and non-deforming nature of the tungsten carbide WC reinforcements, which constricts HSS-particle deformation, sliding and rearrangement during compaction. Additions of 30% tungsten carbide increase the assintered density.

Figure 4 shows that the M3/2 grade HSS cannot be fully densified at 1150C, and that the assintered density is approximately equal to the green density. Additions of 30% tungsten carbide increase the as-sintered density presumably due to the occurrence of a liquid phase resulting from a chemical reaction occurring between the HSS matrix and tungsten carbide particles. As exemplified in Fig. 6, marked specimen expansion followed by its rapid contraction has indicated that the chemical reaction takes place at temperatures between 1080 and 1110C.

64 Tungsten Carbide – Processing and Applications

**3. Results and discussion** 

tungsten carbide WC content

sintered density.

**3.1. Characterization of porous skeletons** 

was calculated by means of the following expression (2):

Wear tracks were analyzed by LM to clarify wear mechanisms.

The friction coefficient was measured continuously during the test, and the wear coefficient

*friction force N <sup>F</sup> load N*

The combined effects of tungsten carbide content and powder processing route on the

relative density and shrinkage of the porous skeleton are shown in Figure 4 and 5.

**Figure 4.** Relative densities of green compacts and pre-sintered porous skeletons as a function of

Figure 5 shows the effect of WC content on compressibility and shrinkage of high speed steel powders. It is evident that green density of compact decreases with increasing WC content. This attributes to hard and non-deforming nature of the tungsten carbide WC reinforcements, which constricts HSS-particle deformation, sliding and rearrangement during compaction. Additions of 30% tungsten carbide increase the as-

Figure 4 shows that the M3/2 grade HSS cannot be fully densified at 1150C, and that the assintered density is approximately equal to the green density. Additions of 30% tungsten carbide increase the as-sintered density presumably due to the occurrence of a liquid phase

[ ]

(2)

[ ]

**Figure 5.** Shrinkage of compacts during sintering as a function of tungsten carbide WC content

**Figure 6.** Dilatometric curves recorded on heating the M3/2 and HSS M3/2 + 30% WC material to the sintering temperature

Figures 4 and 5 show the morphologies of capillaries in both green compacts and presintered skeletons.

Tungsten Carbide as an Addition to High Speed Steel Based Composites 67

Direct infiltration of as-sintered skeletons with copper results in the highest densities. This may be result of deoxidation powder particle surfaces during sintering in vacuum. Figure 10

show the final Cu content in as-infiltrated high speed steel based composites.

**Figure 9.** Relative densities of as-infiltrated composites

**Figure 10.** Copper content in as-infiltrated composites.

**Figure 7.** The morphologies of capillaries in M3/2 grade HSS, SEM

**Figure 8.** The morphologies of capillaries in M3/2 HSS + 30% WC , SEM

From the microstructural observations (Figures 7 and 5) it may be concluded that the morphologies of capillaries are mainly affected by the manufacturing route and powder characteristics (Fig. 1), such as powder particle size and morphologies of powder particles.

Finally, the porous skeletons were vacuum-infiltrated by gravity method at temperature: 1150C for 15 min.
