Growth Of Second-phase Particles Research Articles

Effects of multistage thermomechanical treatment on the microstructure and properties of Cu–Ni–Co–Si–Mg alloy strip by HCCM horizontal continuous casting

Multistage thermomechanical treatment experiments were conducted on Cu–Ni–Co–Si–Mg alloy strip prepared by the Heating Cooling Combined Mold (HCCM) horizontal continuous casting-cold rolling process. Effects of various heat treatments on the microstructure, mechanical properties, and electrical conductivity of the alloy were studied. The strengthening mechanisms and factors influencing the performance of each process has been analyzed. The tensile strength, yield strength, and electrical conductivity of Cu–Ni–Co–Si–Mg alloy can reach 894 MPa, 855 MPa, and 47.1 %IACS after a third-stage of thermomechanical treatment (TTMT). The cold rolling in first-stage of thermomechanical treatment (FTMT) not only caused work hardening of the alloy but also promoted the precipitation of solute atoms and the growth of second phase particles, limiting the increase in strength. Second-stage of thermomechanical treatment (STMT) effectively hindered the excessive growth of second phase particles in FTMT but shortened recrystallization process. The superior performance of Cu–Ni–Co–Si–Mg alloy after TTMT was attributed to dispersive precipitation of Ni, Co, and Si elements as (Ni, Co) 2Si phases in the copper matrix, strengthening the interaction between the precipitates and dislocations. A short process of HCCM horizontal continuous casting-cold rolling-thermomechanical treatment was developed to produce a high strength and highly electrically conductive Cu–Ni–Co–Si alloy strip used in lead frames.

Influence mechanism of solution temperature on microstructure evolution and tensile properties of Ti microalloyed high strength steel CGLC700

The influence mechanism of solution temperature on the strength and toughness of Ti microalloyed steel CGLC700 was studied. The microstructure changes of Ti microalloyed steel were observed by micro-electron microscopy, and the mechanical properties were evaluated by tensile test. The appropriate solution temperature can promote the solid solution of Ti atoms and the formation of small-sized TiN, TiC and other particles, hinder the movement of dislocations, and improve the tensile properties of steel. When the solution temperature is 1240 °C (2#), the grain size of steel is the lowest, the proportion of high angle grain boundary is the highest, and the tensile properties of steel are the best. Ti microalloyed steels increased tensile strength by 4.12%, yield strength by 2.85% and elongation by 28.4%. Too low or too high solid solution temperatures weaken the strengthening effect of the microalloying elements and led to a reduction in the tensile properties of the steel. This can be attributed to the low solid solution of Ti at low solid solution temperatures and the growth of second phase particles and inclusions at too high solid solution temperatures. This study provides a theoretical basis for optimizing the heat treatment process of Ti microalloyed steel.

Mitigating the Recrystallization of a Cold-Worked Cu-Al2O3 Nanocomposite via Enhanced Zener Drag by Nanocrstalline Cu-Oxide Particles.

The strength of metals and alloys at elevated temperatures typically decreases due to the recovery, recrystallization, grain growth, and growth of second-phase particles. We report here a cold-worked Cu-Al2O3 composite did not recrystallize up to a temperature of 0.83Tm of Cu. The composite was manufactured through the internal oxidation process of dilute Cu-0.15 wt.% Al alloy and was characterized by transmission electron microscopy to study the nature of oxide precipitates. As a result of internal oxidation, a small volume fraction (1%) of Al2O3 particles forms. In addition, a high density of extremely fine (2-5 nm) Cu2O particles has been observed to form epitaxially within the elongated Cu grains. These finely dispersed second-phase Cu2O particles enhance the Zener drag significantly by three orders of magnitude as compared to Al2O3 particles and retain their original size and spacing at elevated temperatures. This limits the grain boundary migration and the nucleation of defect-free regions of different orientations and inhibits the recrystallization process at elevated temperatures. In addition, due to the limited grain boundary migration, a bundle of stacking faults appears instead of annealing twins. This investigation has led to a better understanding of how to prevent the recrystallization process of heavily deformed metallic material containing oxide particles.

The synthesis of TiC dispersed strengthened Mo alloy by freeze-drying technology and subsequent low temperature sintering

The TiC dispersed strengthened Mo alloys were synthesized by novel freeze-drying technology and subsequent low-temperature sintering. With the introduction of TiC nanoparticles using freeze-drying technology, the sintered Mo-TiC alloys possess ultrafine grain size (2.38 μm), high density (99.3%) and high hardness (402±29 HV0.2). The agglomeration and growth of second phase particles in Mo-TiC alloys were effectively depressed by freeze-drying technology. Moreover, a theory about purification and strengthening is proposed. C-deficient TiC (Ti8C5) will adsorb nearby oxygen impurities and even form TiO2 to purify Mo matrix. Furthermore, TiC (002), Ti8C5 (0-24) and TiO2 (111) can form coherent interfaces with Mo (110) to strengthen their phase boundary and improve material strength. The stable phase interface can pin and limit the growth of these second phase particles, thus maintaining their small size (<50 nm).

Effect of the Second-Phase Particle Precipitation on the Recrystallization Texture of High-Strength and Fine-Grain Interstitial-Free Steel

The effect of the second-phase particle precipitation on the recrystallization texture of high-strength and fine-grain interstitial-free steel was studied. It is shown experimentally that the sizes of second-phase particles increase and their number decreases with holding time and annealing temperature. The texture is mainly influenced by the size, number, and distribution of the particles. Finely dispersed second-phase particles are strongly pinned on the grain boundaries, which significantly hinders the development of {111} surface textures. It the pinning force on the grain boundary decreases, the {111) surface texture improves due to the aggregation and growth of second-phase particles with holding time. The strength of the γ-phase ({111}<112> texture) grows and reaches maximum (annealing temperature 850°C), finally declines with annealing temperature. Precipitated particles of 40–60 nm favor the development of the {111} texture component.

High-Temperature Precipitation of Impurities within the Vlasov Model for Solids

It is shown that the Vlasov model for a solid describes the complexing processes when growing real crystals with allowance for the thermal growth conditions. It makes it possible (along with the classical theory of nucleation and growth of second-phase particles in solids) to calculate the defect crystal structure that was formed during the growth. It is established that the high-temperature impurity precipitation is directly related to the subsequent transformation of the defect structure when manufacturing of silicon devices. A qualitative model of the formation of electric centers is proposed, which directly relates their origin to the initial defect structure of silicon. It is shown that the concepts and principles of the Vlasov physics are absolutely applicable in solid-state physics.

Aging Treatment on the Microstructures and Mechanical Properties of New Groove T92/Super 304H Dissimilar Steel Joints

AbstractThe effect of aging treatment on the microstructures and mechanical properties of new groove T92/Super 304H dissimilar steel joints is studied in this paper. The experimental results show that the heat-affected zone (HAZ) of T92 is mainly composed of coarse-grained and fine-grained martensitic, whereas the microstructure of Super 304H HAZ and weld seam exhibit an austenitic structure. Aging treatment increases the nucleation and growth of second phase particles of the weld joints, especially at T92 side. The weld joints have a low tensile strength (&lt;700 Mpa) and a high tensile strength (&gt;700 Mpa) when the tensile fractures are located at weld seam and T92 base metal, respectively. With increasing aging time, the hardness and tensile strength of the weld joints initially decrease, then increase, and finally stabilize. Moreover, the weld joints have a maximum hardness value at the T92 heat-affected zone. At room temperature condition, the impact absorbed energy reaches the minimum value, which is related to the coarse grain containing equiaxed dendrites in the weld seam.

On the problem of the consistency of the high-temperature precipitation model with the classical nucleation theory

The adequacy of the model of high-temperature precipitation in dislocation-free silicon single crystals to the classical theory of nucleation and growth of second-phase particles in solids has been considered. It has been shown that the introduction and consideration of thermal conditions of crystal growth in the initial equations of the classical nucleation theory make it possible to explain the precipitation processes occurring in the high-temperature range and thus extend the theoretical basis of the application of the classical nucleation theory. According to the model of high-temperature precipitation, the smallest critical radius of oxygen and carbon precipitates is observed in the vicinity of the crystallization front. Cooling of the crystal is accompanied by the growth and coalescence of precipitates. During heat treatments, the nucleation of precipitates starts at low temperatures, whereas the growth and coalescence of precipitates occur with an increase in the temperature. It has been assumed that the high-temperature precipitation of impurities can determine the overall kinetics of defect formation in other dislocation-free single crystals of semiconductors and metals.

Long-time hot strength of nickel-base alloys

1. The coalescence of particles of second phase, precipitated from solid solution, proceeds at diminishing rate during the aging at high temperature of nickel-base alloys. At constant aging temperature, the rate of this process is determined by the composition. 2. Boron accelerates growth of second phase particles (alloys 1 and 2). The increased al uminum content in alloy 3 decreases the mean growth rate of the particles. 3. At any particular aging time, a variety of particle sizes exists. However, particles of a certain size predominate. 4. There is a definite correspondence between the growth rate of particles and the time variation of the rupture strength. Hence structural changes have an important effect on the change of rupture strength with time.