PSI - Issue 65

E.G. Zemtsova et al. / Procedia Structural Integrity 65 (2024) 310–316

315

E.G. Zemtsova et al. / Structural Integrity Procedia 00 (2024) 000–000

6

An important feature of the developed composite is the absence of explicit interface boundaries between the metal matrix and the reinforcing element. This ensures the binding of the matrix and the reinforcing phase into a single whole. The atoms of the reinforcing phase and the matrix material, connected to each other by chemical bonds through a conditional interface plane, belong simultaneously to two coordinated structures, as a result of which the formed conditional interface is characterized by low energy and, consequently, high strength and plasticity.

2.2. Mechanical uniaxial stretching tests

During the work, we obtained a composite from a Ni matrix reinforced with 5% of Ni/Al-TiC, a composite of a Ni matrix reinforced with 5% TiC (particle size 20 microns), a composite of Ni matrix reinforced with 5% TiC (particle size 0.2 microns). Their mechanical properties were identified (Table 2).

Table 2. Ni-matrix based composite samples Sample No. Reinforcing phase

Reinforcing phase amount, wt. %

Ultimate strength σ, MPa

Ɛ, %

Plasticity limit MPa, σ_02, exp.

at 200°C

1 2 3 4

No

-

256 365 287 248

14 15 11 10

80 91 70 64

Ni/Al - TiC, 2 nm TiC, 20 micron TiC, 0.2 micron

5 5 5

Despite the small volume fraction of TiC in the structure of a Ni composite, carbides have a significant effect on strength properties. The manufactured samples with the Ni/Al–TiC reinforcing phase showed strength characteristics significantly superior to those with micron reinforcing carbide phases, while the plasticity remained at the level of pure Ni. This hardening is achieved due to the absence of phase boundaries between the Ni matrix and the nanostructured reinforcing phase. This ensures the binding of the matrix and the reinforcing phase into a single whole and allows for a uniform distribution of the particles of the reinforcing phase in the Ni matrix to avoid their agglomeration into larger structures. Nanostructures of TiC with a size of about 2 nm are formed on the surface of Ni particles. These nanostructures of TiC at the boundaries of Ni grains during sintering of the Ni matrix prevent the recrystallization of the matrix and contribute to reducing the grain size of the matrix itself. The processes of hardening of materials occurring in this case are in good agreement with the Hall-Petch mechanisms. In addition, TiC nanostructures, interacting with the grain boundaries of the matrix, prevent the movement of these boundaries and the sliding of dislocations. This also explains the significant increase in tensile strength and increase in yield strength for sample 2 containing nanostructured TiC. At the same time, the increase in tensile strength is influenced by the formation of local Guinier-Preston zones at the boundary of the Ni matrix and the sublayer of Al atoms of the reinforcing phase (Ni/Al–TiC). The hardening of the composite occurs due to the penetration of Al atoms into the Ni matrix during sintering of the sample (1100 °C). The radii of Ni atoms is 0.124 nm, Al is 0.143 nm. Ni-based composites reinforced with micron TiC particles, have disadvantage of uniform reinforcing phase distribution in the matrix and an aggregation problem. Aggregates provoke the appearance of internal defects and pores in the Ni matrix, which significantly reduces the strength and plasticity of such composites. A combined approach has been developed in the production of metal matrix composites based on surface nanostructuring of the reinforcing phase and bulk matrix reinforcement. A composite with a reinforcing phase was obtained from TiC nanostructures on Ni with a size of about 2 nm, which are evenly distributed in the bulk matrix. This is due to the strength of the interphase boundaries between the matrix and the reinforcing phase due to the presence of chemical bonds between them. The composite, which uses a reinforcing phase with surface carbide nanostructures on the surface of Ni particles to harden, in addition to a higher tensile strength (1.5 times higher than that of a Ni matrix), demonstrates a more plastic fracture pattern characteristic of dispersed hardening of materials. 3. Conclusion