PSI - Issue 35

Aleksandr Zemlianov et al. / Procedia Structural Integrity 35 (2022) 181–187 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

184

4

During cooling all B 1 , B 2 , B 3 and B 4 are free surfaces. Tension of the coated material in the X 1 -direction is simulated by kinematic boundary conditions on the B 1 and B 3 surfaces, while B 2 and B 4 surfaces are free from loads. Coating layers (Fig. 1b) composed of the Al6061T6 aluminum matrix reinforced by boron or tungsten carbide particles were arranged in two combinations: B 4 C top layer – WC bottom layer and, vice versa, WC top layer – B 4 C bottom layer. For the sake of generality, the composite coating, where both layers are reinforced by B 4 C particles, is also included into consideration for comparison. Experimental mechanical properties of the aluminum alloy and reinforcing particles are shown in Table 1.

Table 1. Mechanical properties of the compound materials.

Material

ρ, g/cm 3

µ

K, GPa

σ

S , MPa

σ 0,2 , MPa

α, 10 °C -1

C ten , GPa

C com , GPa

ε p

r , %

-6

Al6061T6

2.7 2.6

26

66

332

234

22

-

-

9.5

B 4 C WC

197 260

235 370

- -

- -

4.5

0.5

5 5

- -

15.6

5

0.37

3. Results and discussions The results of numerical simulation are presented in Figures 2-4. Figure 2 shows a comparison of the stress states with and without preliminary cooling of the bi-layer coated material with «WC top layer - B 4 C bottom layer» arrangement of the coating layers. Figure 3 shows the plastic strains in the matrix and particle cracking for varying arrangement of layers, with and without taking into account residual stresses. Figure 4 shows the calculated stress strain curves corresponding to these cases.

Fig. 2. Equivalent stress in bi-layer coated material with WC top – B 4 C bottom coating layer arrangement under tension (a) and cooling followed by tension of the structure shown in Fig. 1b (b). Total strain of the coated material is 0.06%.

Under cooling of the coated material residual stress concentrations are formed in both the matrix and particles (Fig. 2b). It was shown that the regions of residual stresses are rounded regions localized in the matrix near the «matrix-particle» interfaces. High stresses concentrate near the interfacial asperities (Fig. 2b, Al6061T6 Matrix). Stresses in ceramic particles are higher than in the matrix (300 MPa versus 200 MPa maximum stresses), with the highest values being located near the coating-substrate interface (Fig. 2b, Ceramic particles). Fracture of particles begins even during cooling, i.e. fractured particles are observed even at a small tensile deformation of 0.06%.