Metal Science and Heat Treatment最新文献

Influence of thermal aging (873 K, 5000 h) on microstructure and tensile-plastic flow behavior of normalized and tempered (N&T) 1.4W – 0.06Ta IN-RAFM steel is investigated. The Ludwigson and Voce equations are used to elucidate the tensile-plastic flow response of the IN-RAFM steel over a wide temperature range of 298 – 873 K. Both the yield strength and the tensile strength are fitted by the initial stress and saturation stress, respectively, as per the Voce constitutive equation. The strain hardening exponent increases under aging due to the increase in the work hardening capability of the aged steel, while the strain hardening coefficient decreases with the aging. TEM specimens extracted from a tensile tested sample are used to correlate the formation and the movement of dislocation debris in the structure of both N&T and thermally aged steel. The absolute value of n_v decreases due to the aging exhibiting a two-stage behavior. The acceleration of the recovery process is lower at the high temperature in the steel subjected to thermal aging as compared to the N&T steel. The Voce relation is used successfully to predict the yield stress and the ultimate tensile strength of both thermally aged and N&T IN-RAFM steel at different temperatures.

Steel 30KhGSA is studied after a quenching and partitioning (Q&P) heat treatment and after traditional quenching. Structural and x-ray analyses are performed and mechanical properties are determined. The Q&P treatment produces a martensite-austenite structure with 10 vol.% retained austenite. The use of Q&P instead of the traditional quenching elevates the impact toughness by a factor of 3 and the resistance to fatigue crack growth by a factor of 2. A long hold at room temperature (for more than a month) reduces the content of retained austenite in the Q&P-steel to 7.5 vol.% and lowers its impact toughness and crack resistance by a factor of 1.5 as compared to the state right after the hardening.

The process of argon arc welding of nickel onto titanium with a nonconsumable electrode with feeding of the nickel filler wire into the liquid metal pool is investigated. The influence of the welding modes on the geometrical parameters of the bead and on the susceptibility of the forming surface layer to crack formation is described. The effect of the welding modes on the chemical and phase compositions of the formed surface layer of titanium nickelide is determined. The chemical and phase compositions of the welded-on layer are shown to affect its hardness and wear resistance.

The possibility of using a special type of Friction Stir Welding (FSW) – Friction Hydro Pillar Processing (FHPP) to manufacture a joining between dissimilar materials (high-carbon ductile iron FE55006 and low-carbon steel SAE 8620) is studied. The macrostructure, microstructure, microhardness and residual stresses of the welded joint are determined. The efficiency of using the FHPP technology for obtaining high-quality joints from dissimilar iron-based alloys is demonstrated. It is established that such joints have a high hardness due to the formation of a martensitic structure in the alloys during their processing by the FHPP method.

The orientation relationships between the β-phase and the S2 silicides (Ti, Zr)₆Si₃ (a = 0.7055 nm, c = 0.3673 nm) in titanium pseudo-β-alloy VT47 are studied. The distribution of the crystallographic directions on an inverse pole figure in the β-phase coordinates is presented. A large sample of silicides is studied, and absence of single orientation relationships between the β-phase and the S2 silicides in the alloy after rolling and annealing is inferred. Variants of nucleation of S2 silicides are considered on the basis of the theory of nucleation and of data on the Ti – Zr – Si system. Amechanism of the loss of β/S2 orientation relationships in the process of thermomechanical treatment of the alloy is suggested. The Ti/Zr proportion at a constant content of Si is shown to grow with the sizes of the silicides. The silicide particles affect the initial aging state of alloy VT47. They serve free surfaces for nucleation and growth of β-phase during aging and make its distribution more uniform.

Special features of structural and phase transformations occurring in annealing of an explosion-welded Al – Zr bimetal are considered. It is shown that heat treatment causes formation and growth of an intermetallic layer on the interface, which has a hardness of 9 GPa. The methods of microscopic x-ray spectrum analysis and of phase analysis with the use of synchrotron radiation are used to show that the intermetallic layer is represented by a ZrAl₃ phase with a D0₂₃-type structure. The lattice constants of this phase vary gradually from the metal-intermetallic interfaces to the center of the layer. Quantum-chemical modeling by the method of density functional is used to show that the zirconium trialuminide is in the steadiest state at a certain distance from the interface due to the process of secondary recrystallization and the accompanying annihilation of crystal structure defects.

The effect of the number of passes during friction stir processing on the structure and properties of the surface layers of aluminum alloy 5083 is investigated. The alloy is processed by the FSP method with one, two and four passes, after which the tensile strength, the elongation under static tension, the impact energy during dynamic bending and the microhardness are determined. After a single-pass FSP, a significant increase in the elongation of the material is observed. However, with increase in the number of passes, its plasticity decreases slightly, remaining above the initial value. It is shown that after FSP, the microhardness of the alloy increases, and the tensile strength and the impact energy decrease, and these changes become more significant with increase in the number of passes.