Papers by Keyword: Dispersed Particles

Abstract: The work addresses the microstructural evolution and mechanical properties of the ultrafine-grained (UFG) VT8M-1 subjected to isothermal die forging (IDF) and subsequent thermal treatment. An UFG microstructure with a mean size of secondary grains of about 0.3 μm was processed by a rotary swaging (RS) at Т=780°С. The ultimate tensile strength (UTS) of the alloy increased by 23% as compared to an initial state due to the formation of an UFG microstructure. It has been shown that isothermal die forging of the UFG alloy at Т=780°С leads to the growth of secondary phase grains by 0.7 μm. Subsequent heat treatment of the forged billets leads to hardening of 11%, which can be attributed both to the formation of additional interphase α/β boundaries at the precipitation of a tertiary α-phase and silicide dispersion.

Abstract: One of the main processes in metal products is heat treatment. However, existing regimes of heat treatment are not suitable for the new gradient metals. This article presents a method of obtaining gradient metallic materials and heat treatment development. Also presents the studies results of heat treatment effect on mechanical properties and metal structure.

Abstract: This paper describes experiments on the introduction of fine particles in the melt is crystallized in the preparation of centrifugally cast billets. To predict the distribution of particles in the crystallizing melt was conducted mathematical modeling of the process. To confirm the data obtained by mathematical modeling experiments were conducted to obtain a centrifugal-cast billets with the introduction of fine particles. The investigation of the microstructure of the samples obtained. Comparing the data obtained about the conduct of computer simulation and real experiment, the distribution of particles in the melt crystallizing. In conclusion, this article presents the findings of the work done.

Abstract: The thermoelastic martensitic transformations, shape memory effect and superelasticity in high-strength single crystals of ferromagnetic FeNiCoAlX (X = Ta, Nb, Ti), CoNiGa, NiFeGaCo alloys and TiNi alloy in monophase and heterophase states with nanoscale dispersed particles are investigated. The dependences of the thermal and stress hysteresis, superelasticity temperature range, reversible transformation strain on the size of the dispersed particles, crystal orientation, stress state, level of applied stress and test temperature are obtained. The criteria of high-temperature superelasticity and the conditions for narrow thermal and stress hysteresis, large value of reversible transformation strain, which exceeds the theoretical lattice strain, are established. The thermodynamic description of the effect of particles on the stress-induced martenstic transformation in single crystals of new high-ferromagnetic alloys are elaborated.

Abstract: In the present study the effect of second γ'-phase particles which do not undergo martensitic transformation on the functional properties – shape memory effect and superelasticity, in ferromagnetic FeNiCoAlX (X = Ta, Nb, Ti) and NiFeGaCo single crystals are investigated. Dispersed γ'-phase particles allow to control both mechanical and functional properties due to variation of chemical composition, volume fraction and size of nanoparticles, and to obtain the nanocomposites with complex of necessary properties.

Abstract: Effect of carbide precipitation on pinning force and migration mechanism of boundaries of martensite laths was considered in a 3%Co modified P911. The dimensions of second phase precipitations, martensite laths and dislocation densities were measured by means of transmission electron microscopy. The pinning forces retarding the motion of the lath boundaries, that arise from M(C,N) nanoscale precipitations and M₂₃C₆ particles were evaluated by using different models. The pinning pressure evaluated by taking into account a non-uniform distribution of M₂₃C₆ particles was high enough to stabilize the lath martensite structure during tempering and long term ageing. On the other hand, significant coarsening of martensite laths occurred in neck portions of samples subjected to long-term creep tests. Additional effects from dislocation density and applied stress on the motion of lath boundaries are considered in some details.

Abstract: Microstructure evolution in a P911 heat resistant steel was examined under conditions of aging and creep at a temperature of 600°C and an applied stress of 200 MPa. The tempered martensite lath structure (TMLS) evolved after heat treatment consisted of prior austenite grains (PAG), packets, blocks and laths. The mean transverse lath size and the interior dislocation density were about 345 nm and 3.5 × 10¹⁴ m^-2, respectively. Various second phase particles precipitated upon tempering. Fine MX carbonitrides were homogeneously distributed throughout the tempered martensite laths, while relatively coarse M₂₃C₆ carbide particles were located on high-and low-angle boundaries. Upon creep test, precipitation of Laves phases was found. The stability of TMLS during creep is discussed in detail.

Abstract: By using vacuum melting, nitrogen protection and a high molten flow rate during pouring, many nano-TiN particles with the size of 20~100nm are formed during solidification of the alloy steel composed of C0.12- Si0.24 - Mo0.45 - Cr0.35 - V0.2 - Ti0.29 (wt.%). In addition, there are 0.9-1.4μm micron-sized particles separated by a space of 15~40μm. Precipitable TiN particles greatly refine the microstructure of the alloy steel. In this paper, the thermodynamic, kinetic mechanisms and related factors of TiN formation are analyzed.