**3.2. Characterization of as infiltrated materials**

The as-infiltrated properties of the investigated composites are a complex function of the manufacturing route and tungsten carbide content. The properties of the as-infiltrated composites are shown in Figures 9÷12.

From Figure 9 it is evident that the molten copper is drawn into the interconnected pores of the skeleton, through a capillary action, and fills virtually the entire pore volume to yield final densities exceeding 97% of the theoretical value. In all cases, the additions of tungsten carbides aren't causes in the final density of the materials as compared with the base material. 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

66 Tungsten Carbide – Processing and Applications

**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

**3.2. Characterization of as infiltrated materials** 

composites are shown in Figures 9÷12.

sintered skeletons.

1150C for 15 min.

Figures 4 and 5 show the morphologies of capillaries in both green compacts and pre-

green compact pre-sintered skeleton

green compact pre-sintered skeleton

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:

The as-infiltrated properties of the investigated composites are a complex function of the manufacturing route and tungsten carbide content. The properties of the as-infiltrated

From Figure 9 it is evident that the molten copper is drawn into the interconnected pores of the skeleton, through a capillary action, and fills virtually the entire pore volume to yield final densities exceeding 97% of the theoretical value. In all cases, the additions of tungsten carbides aren't causes in the final density of the materials as compared with the base material.

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

From Figure 10 it is evident that the copper content in as-sintered materials is lower than in infiltrated green compacts. It is affected by densification during sintering of porous skeletons.

Tungsten Carbide as an Addition to High Speed Steel Based Composites 69

The Brinell hardness of the as-infiltrated composites increases with the percentage of additions of tungsten carbide WC. Considerable differences in hardness between the materials obtained from the two infiltration routes have been observed, with higher hardness numbers achieved with direct infiltration of green compacts, this can be explained

The Bending Strength of the as-infiltrated composites decreases with the increased content of tungsten carbide WC in the starting powder mix. For pre-sintered samples made of M3/2 – tungsten carbide mixture an increase of bending strength occurs; this can be explained by

Typical microstructures of a copper infiltrated green compact and pre-sintered skeleton are

green compact infiltrated with copper pre-sintered skeleton infiltrated with copper

green compact infiltrated with copper pre-sintered skeleton infiltrated with copper

by the diffusion of carbon and alloying of iron particles during sintering.

the chemical reaction between the tungsten monocarbide and HSS matrix.

**3.3. Microstructures** 

shown in Figures 13 – 15.

**Figure 13.** Microstructures of M3/2 HSS based composites

**Figure 14.** Microstructures of M3/2 HSS + 10%WC composites

**Figure 11.** The Brinell Hardness of as-infiltrated composites

**Figure 12.** The Bending Strength of as-infiltrated composites

The Brinell hardness of the as-infiltrated composites increases with the percentage of additions of tungsten carbide WC. Considerable differences in hardness between the materials obtained from the two infiltration routes have been observed, with higher hardness numbers achieved with direct infiltration of green compacts, this can be explained by the diffusion of carbon and alloying of iron particles during sintering.

The Bending Strength of the as-infiltrated composites decreases with the increased content of tungsten carbide WC in the starting powder mix. For pre-sintered samples made of M3/2 – tungsten carbide mixture an increase of bending strength occurs; this can be explained by the chemical reaction between the tungsten monocarbide and HSS matrix.

### **3.3. Microstructures**

68 Tungsten Carbide – Processing and Applications

**Figure 11.** The Brinell Hardness of as-infiltrated composites

**Figure 12.** The Bending Strength of as-infiltrated composites

skeletons.

From Figure 10 it is evident that the copper content in as-sintered materials is lower than in infiltrated green compacts. It is affected by densification during sintering of porous

> Typical microstructures of a copper infiltrated green compact and pre-sintered skeleton are shown in Figures 13 – 15.

**Figure 13.** Microstructures of M3/2 HSS based composites

**Figure 14.** Microstructures of M3/2 HSS + 10%WC composites

It can be seen that the microstructure of the M3/2 grade HSS based composites consists of a steel matrix with finely dispersed carbides and islands of copper. Figures 13 and 15 shows tungsten carbides located within the grains and on the grain boundaries as well. Microstructures show small porosity at both sintering temperatures, and carbides are larger at the pre-sintered skeleton infiltrated with copper, MC carbides being the white ones, while MC carbides are grey. Some free copper areas are also present. In some places, these added carbides are related with white MC carbides, but free copper dark grey is preferentially linked to WC.

Tungsten Carbide as an Addition to High Speed Steel Based Composites 71

green compact infiltrated with copper pre-sintered skeleton infiltrated with copper

Phase identification of the composites was performed by a Tur 62 X-ray diffraction (XRD)

Figure 19 show the XRD patterns of samples M3/2 + 30%WC. They illustrate the existence of the main carbides M6C and MC as well as the existence of ferrite and austenite and the high intensity for the main Cu peak in sample green compact infiltrated with copper compared with sample pre-sintered skeleton infiltrated with copper as well as the higher intensity coming from higher volume of copper in as-infiltrated green compact. It should be noted that the intensity of the Fe3W3C peaks in sample pre-sintered skeleton infiltrated with copper can be explained by the chemical reaction between the tungsten monocarbide and

The SEM and EDX analysis performed on the specimens containing M3/2 10 and 30% tungsten carbide have revealed the carbide phase evenly distributed within the copper-rich regions. As it is apparent from Figures 20 and 21, WC reacts with the surrounding HSS matrix and forms a tungsten and iron-rich M6C carbide grain boundary network during

**Figure 17.** SEM microstructures of M3/2 HSS + 30%WC composites

**4. Phase identification** 

sintering of porous skeletons.

HSS matrix.

machine with Cu target (K, *λ* = 1.5406Å).

**Figure 15.** Microstructures of M3/2 HSS + 30%WC composites

SEM microstructures of a copper infiltrated green compact and pre-sintered skeleton are shown in Figures 16 – 17.

**Figure 16.** SEM microstructures of M3/2 HSS based composites

Tungsten Carbide as an Addition to High Speed Steel Based Composites 71

**Figure 17.** SEM microstructures of M3/2 HSS + 30%WC composites
