PSI - Issue 50

N.B. Pugacheva et al. / Procedia Structural Integrity 50 (2023) 251–256 N.B. Pugacheva et al./ Structural Integrity Procedia 00 (2022) 000 – 000

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Specimens sized 35×5×5 mm were tested for transverse bending in an Instron 8801 servo hydraulic testing machine according to ISO 3327-82. The testing rate was 0.2 mm/min and the distance between the pier axes was 30 mm. Transverse rupture strength R bm 30 was calculated by the formula

2      , 2 b h F l 3

(4)

R

bm

where F is the highest force corresponding to the instant of specimen fracture, N; l is the distance between the pier axes, mm; h is specimen height (the dimension coinciding with the direction of force application during testing), mm; b is specimen width (the dimension perpendicular to the height), mm. 3. Results and discussion The metal matrix of the composite is a copper-based solid solution. The most intensive lines in the diffraction pattern correspond to copper (Fig. 2). Grey TiC particles sized 0.5 to 2 μm have a shape close to spherical (area A in Fig. 1). They are evenly distributed in the volume of the composite (portion 1 in Fig. 3). Darker TiB 2 particles sized 2 to 10 μm have a shape close to cubic (area B in Fig. 1). They are distributed unevenly and form clusters (portion 2 in Fig. 3). It is practically impossible to distinguish areas with only TiB 2 particles in the structure of the composite. There are always TiC particles nearby. Therefore, the electron-probe test of the chemical composition of the composite phases and structural constituents always demonstrated the presence of carbon and boron simultaneously (Table 1). Some regions of the composite retain B 4 C particles, unreacted in reaction (1) (area 3 in Fig. 3). The size of the B 4 C particles ranges between 10 to 35 μm. The number of B 4 C particles in the composite is small; therefore, only the strongest reflections of this phase can be observed by X-ray diffraction analysis (Fig. 2). Thus, the composite under study consists of three structural constituents: 1) Cu+TiC mechanical mixture; 2) Cu+TiB 2 +TiC mechanical mixture, and 3) B 4 C particles. The density of the composite is 6.8 g/cm 3 . The overall hardness is 60 to 62 HRC, and this will certainly provide high values of wear resistance.

Fig 2. The X-ray pattern of the composite.

Fig 1. An SEM image of the Cu-Ti-C-B composite microstructure: A – Cu+TiC mechanical mixture, B – Cu+TiB 2 +TiC mechanical mixture.

The uneven distribution of the strengthening phases in the composite is responsible for the nonuniformity of the micromechanical properties (Fig. 4). The Cu+TiC areas are the most plastic ones (area 1 in Fig. 3). The Cu+TiC load curve is shifted into the region of the highest values of indenter penetration depth h (Fig. 4). For this constituent, there is a small yield plateau when the indenter is held at a maximum load; therefore the plasticity index С IT for the Cu+TiC area is maximum (Table 2). The Cu+TiB 2 +TiC areas are characterized by high microhardness (1006.8 ± 5.9) HV 0.1 and high elastic properties E*, W e , H IT /E* (see Table 2). The Ti+TiB 2 +TiC constituent of the