Correlation of yield strength with internal coherency strains for age-hardened Cu−Ni−Fe alloys

The maximum yield strengths for a given aging temperature were measured for age-hardened Cu−Ni−Fe alloys. The yield strengths were found to be proportional to the difference in cubic lattice parameters of unstressed precipitating phases and independent of other factors such as precipitate particle size and precipitate volume fraction. The yield strength dependence on lattice parameter differences alone indicated coherency stresses controlled the yield strengths. An analysis of the yield strength based only on internal coherency strains and stresses subsequently led to the derivation of an equation for the yield strength,i.e., where is the Taylor factor for converting from single crystal shear stress to polycrystalline tensile stress results,C _ijare single crystal elastic stiffness constants and Δa is the difference in, anda ₀ the average of the cubic lattice parameters of the precipitating phases. The equation indicates the yield strength is dependent only on the internal coherency strains and independent of particle size and precipitate volume fraction, as observed. The correlation of the experimentally measured yield strengths with the equation was quite good.     

Fatigue strength of a Ti–6Al–4V alloy produced by selective laser melting

The fatigue properties and the fracture mechanisms of the Ti–6Al–4V alloy produced by selective laser melting (SLM) from a powder of an CL41TiELI titanium alloy have been studied. Cylindrical blanks were grown at angles of 90° and 45° to a platform. The best fatigue strength is observed in the samples the blanks of which were grown at an angle of 45°. It is found that the structure of the SLM material can contain portions with unmelted powder particles, which are the places of initiation of fatigue cracks.     

Oxidation resistance and strength of a molybdenum fiber–oxide matrix composite material

The oxidation kinetics of a composite material, which consists of an Al₂O₃–Al₅Y₃O₁₂ matrix and molybdenum fibers and has a high cracking resistance, is studied. The mass loss of the composite material during oxidation is shown to be several orders of magnitude lower than that of molybdenum. Oxidation in quiet air at 1250°C for several hours weakly changes the strength of the composite material at temperatures from room temperature to 1300°C. It is also shown that the strength of the composite material as a function of the oxide matrix composition (Al: Y ratio) changes nonmonotonically. The maximum strength shifts from the Al₂O₃–Al₅Y₃O₁₂ eutectic point toward garnet.     

Changes in the fracture strength parameters of ferritic–bainitic and bainitic pipe steels during operation

The fracture strength and the sensitivity to delayed fracture of the pipes in oil-trunk pipelines that are made of ferritic–bainitic and bainitic steels are studied. The results of modeling of the delayed brittle fracture of pipe steel during a simultaneous action of mechanical stresses and a corrosive medium are presented.     

Identification of the modified Drucker–Prager yield condition and modeling of compaction of the plasticized titanium feedstock

A computer modeling procedure of densification of the noncompact titanium feedstock is considered. The modified Drucker–Prager cap model is used to describe the rheological flow of the deformed mass. It is shown that, when identifying the accepted model with the accuracy acceptable for engineering calculations, it is reasonable to use the auxiliary curve based on the Bernoulli lemniscate, which makes it possible to reduce the number of experiments necessary to construct the piecewise-smooth Drucker–Prager yield curve. The plastic deformation of the representative volume cell of sieving the titanium sponge in various deformation modes is investigated. To improve the formability of the noncompact titanium-containing feedstock, the plasticizing effect associated with an increase in the amount of the plastic β-phase upon hydrogen alloying is used. It is revealed based on theoretical and experimental investigations that hydrogen alloying makes it possible to form a denser billet at invariable temperature and compaction force compared with the traditional densification technology of titanium sponge. It is established that the distribution uniformity of relative density over the axial billet section increases with the additional hydrogen alloying. The satisfactory convergence of results of computer modeling and an experimental investigation into the compaction of the titanium sponge in a closed die is shown.     

Z-phase formation and its effect on long-term creep strength in 9–12%Cr creep resistant steels

Precipitation behavior of Z-phase after long-term creep was investigated in ASME Gr.91, Gr.92, Gr.122 and 12Cr steel with delta-ferrite. Many of Z-phase particles were located around prior austenite grain boundaries (PAGBs) and interface between delta-ferrite and martensite after long-term creep. Part of MX cabonitrides around PAGB and the interface disappeared due to the Z-phase formation, indicating that the deformation resistance around PAGB and the interface is low. Time-Temperature-Precipitation (TTP) diagrams of Z-phase were obtained for all steels examined. The time for nucleation of Z-phase was shorter in higher Cr steel. In order to retard the Z-phase formation, the Cr content of the steel should be reduced. Creep strength abruptly decreases in higher Cr steel since the increase in Cr content promotes Z-phase formation together with disappearance of MX carbonitrides. Many of Z-phase particles formed around PAGB in fine-grained heat-affected zone (FGHAZ) of welded joints after long-term creep. The size of Z-phase was similar to those of M₂₃C₆ and Laves phase after creep. For FGHAZ, the number density of Z-phase particles in Gr.122 was four times higher than that in Gr.92. The creep strength of welded joint of Gr.122 was lower than that of Gr.92, indicating that a large number of Z-phase in Gr.122 contributes to decrease in creep strength.     

Influence of alternating cold flexure on the properties of low-alloy pipe steel (strength class K56–K65)

In laboratory conditions, the cold straightening of thick (17.5 mm) low-carbon low-alloy steel sheet (yield point no less than 550 N/mm²) is simulated by alternating flexure. The influence of the number of cycles and the strain in alternating flexure on the strength of the steel is studied. For industrial production on the 5000 mill at OAO Vyksunskii Metallurgicheskii Zavod (VMZ), the influence of the cold-rolling conditions on the yield point and strength of thick (15–23 mm) steel sheet (strength class K56–K65) is demonstrated.     

Microstructure and yield phenomenon of an extruded Mg-Y-Cu alloy with LPSO phase

A yield phenomenon was firstly reported in an extruded Mg-6.8Y-2.5Cu alloy and the corresponding microstructure was also investigated in this work,The cast alloy is mainly composed of α-Mg,18R long period stacking order(LPSO) phase,eutectic phase(Mg₂₀Cu₄Y₁),and Mg₂Cu phase.The 18R LPSO phase at the dendritic grain boundary transforms into the 14H LPSO phase in the grain interior during homogenization.After extrusion,the grain size of the homogenized al...     

Temperature–Composition Dependence of Thermodynamic Mixing Functions of Co–Cr–Cu–Fe–Ni Melts

Powder Metallurgy and Metal Ceramics - In the framework of the CALPHAD method, a thermodynamic database was developed for calculating the thermodynamic properties of liquid alloys in the...     

Features of the Sintering of Fe–Cu–Sn–Ni and Cu–Ti–Sn–Ni Powders during Hot Pressing

Powder Metallurgy and Metal Ceramics - The efficiency and durability of a diamond tool fabricated using powder metallurgy methods depend on several factors. These are the quality of diamond...     

Solidification Behaviour of Ti–Cu–Fe–Co–Ni High Entropy Alloys

For the first time, we report here that the development of the novel Ti?CCu?CFe?CCo?CNi high entropy alloys (HEAs) via vacuum arc melting technique using non consumable tungsten electrode under high purity Ar atmosphere on a water-cooled copper hearth. Ti?CCu?CFe?CCo?CNi multicomponent alloys with varying Ti/Cu (x) molar ratio (x?=?1/3, 3/7, 3/5, 9/11, 1, 11/9 and 3/2) have been prepared through the tailoring of microstructure to get understanding of the phase formation and the microstructural evolution of these multicomponent HEAs. X-ray diffraction and scanning electron microscopy coupled with energy dispersive spectroscopic results confirm the presence of (Cu)_ss, (Co)_ss and (??-Ti)_ss dendrites with ultrafine eutectic between cubic (Cu)_ss and Laves phase (Ti₂Co type). The solidification pathways of novel alloys are critically discussed as follows. For x?=?9/11, 1, 11/9 and 3/2; firstly, (??-Ti)_ss dendrite is formed from the liquid, followed by the liquid phase separation between the cobalt-rich solid solution (Co)_ss and copper-rich solid solution (Cu)_ss and finally, the remaining liquid undergoes eutectic reaction between copper solid solution (Cu)_ss and the Laves phase (Ti₂Co Type), whereas for x?=?1/3, 3/7 and 3/5; (??-Ti)_ss dendrite is formed first from the liquid and then remaining liquid undergoes the liquid phase separation resulting two different dendrites of (Cu)_ss and (Co)_ss phases. Detailed thermodynamic calculations have been carried to rationalize the formation of stable solid solution phases of these newly developed multicomponent Ti?CCu?CFe?CCo?CNi HEAs.     

Simulation and verification of core–shell MC carbide design in Fe–C–Ni–V–Ti steel

Thermodynamic theory was used to calculate the formation temperature and site fraction of MC carbides in Fe–C–Ni–V–Ti system. The calculation results showed the...     

Solid-State Reactions of SiC–TiO2–MgO System and Phase Relations in SiC–SiO2–TiC–TiO2–MgO System

Powder Metallurgy and Metal Ceramics - Preliminary experiments revealed solid-state reactions in the SiC–TiO2–MgO system that resulted in forming TiC compound, providing, thus, a new...     

Processability and Structure Formation of the Al–Zn–Mg–Ca–Fe–Zr–Sc Alloy upon Hot Rolling and TIG Welding

Russian Journal of Non-Ferrous Metals - Technological regimes for producing wrought products (2 and 1 mm) from the Al–4.5%Zn–2.5%Mg–2.5%Ca–0.5%Fe–0.2%Zr–0.1%Sc...     

Iron–Chromium Precursors for Hard-Magnetic Fe–Cr–Co Alloys

The effect of the chromium concentration on the magnetic properties of Fe–Cr precursors for hard-magnetic Fe–Cr–Co materials is studied. Nitrogen used as a sintering atmosphere and a long annealing time enhance are found to increase the coercive force H_c of the materials. The phase formation in Fe–30% Cr alloys is traced during heat treatment in nitrogen and argon atmosphere using thermal analysis.     

粉末锻造Fe–Ni–Cu–C–Mo齿轮材料热处理及性能研究

对Fe–Ni–Cu–C–Mo粉末锻造材料的锻后热处理工艺进行了研究,通过动态连续冷却转变试验绘制出该材料的连续冷却转变（continuous cooling transformation,CCT）曲线,指导材料锻后冷却工艺的选取。对Fe–Ni–Cu–C–Mo淬火试样进行不同温度的低温回火试验,探究不同回火温度对该材料微观组织与力学性能的影响。结果表明,当锻后冷却速率大于7.0 ℃·s?1时,Fe–Ni–Cu–C–Mo粉锻材料组织全为马氏体,硬度趋于稳定;在150 ℃和175 ℃回火,碳化物均匀地分布在马氏体板条内部,起到析出强化的作用,材料表现出优异的抗拉性能。     

Effect of gadolinium on the properties of Pr–Dy–Fe–Co–B materials

Sintered (Pr_1–x–y Dy _x Gd _y )_13–14(Fe_1–z Co _z )_balB_6–7 materials (x = 0.18–0.58, y = 0.05–0.33, z = 0.2–0.36) have been studied. The magnetic moments of gadolinium ions and those of the sublattice formed by Fe and Co ions are shown to be ordered antiferromagnetically. It is noted that an increase in the content of gadolinium, which substitutes for dysprosium, leads to an increase in residual induction B _r , a decrease in coercive force H _cJ , and an increase in the absolute value of the temperature coefficient of induction. The opposite effect takes place in the case of substitution of gadolinium for praseodymium in materials with a fixed dysprosium content.     

Sintering Behaviour and Mechanical Properties of Al–Cu–Mg–Si–Sn Aluminum Alloy

The present study investigates the effect of compaction pressure and sintering temperature on densification response and mechanical properties of the Al–3.8Cu–1Mg–0.8Si–0.3Sn (2712) alloy. The compacts were pressed at 200 and 400 MPa and sintered at temperatures ranging from 570–630°C in vacuum (10^?6 Torr). The objective of the present work is to obtain an optimum sintering conditions for achieving higher sintered densities and mechanical properties. The effect of sintering temperature is evaluated by measuring the sintered density, densification parameter, microstructure, phase changes and mechanical properties. While a higher sintering temperature results in densification enhancement, it also leads to microstructural coarsening. Significant improvement in mechanical properties is obtained through age-hardening of sintered alloy under various ageing conditions (T4, T6 and T8).