Hot Working Of Alloy Research Articles

Effect of Alloying Elements on Strengthening Phase and Solidification Structure of Ti-Al-Mo-Zr Titanium Alloy

This paper mainly studies the composition of strengthening phase, characteristic precipitation temperature and composition range of strengthening phase in Ti-Al-Mo-Zr-Si medical titanium alloy, and the influence of element changes on the content and microstructure of strengthening phase. Promote the formulation of thermodynamic process of titanium alloy powder metallurgy, as well as the formulation of alloy hot working and solid solution aging process. In this paper, Panda thermodynamic software is used to calculate the multicomponent alloy thermodynamics and multicomponent phase diagram of titanium alloy materials. The effects of Al, Mo, Zr, Si and other elements on the precipitation of strengthening phase and the phase transformation content of solidification structure were obtained. It is found that the content of Mo is more than 2 wt.% β phase transition precipitation angle. Meanwhile, in order to avoid the excess of precipitates such as Mo5Si3 and M3Si, the content of Mo should be less than 4.6 wt.%. The content of Zr can be maintained at about 1.5 wt.%. If the aging precipitation of the material is considered, it can be controlled to be less than 2 wt.%. The content of this paper is the basis and improvement of titanium powder metallurgy technology and rapid prototyping technology.

Hot Workability and Microstructure Control of Aluminum-2.5 Copper-1.5 Magnesium Alloy

Aluminum-2.5 copper-1.5 magnesium alloy is an important aerospace alloy and is extensively used in the fabrication of aerospace and aircraft systems. Hot working parameters for the alloy have been generated through hot isothermal compression testing at different temperatures (673–748 K at an interval of 25 K) and at strain rates of 0.01 to 10 s−1. Hot workability of alloy has been established by using the instability criteria and validating the same with microstructural evolution. Further, the Holloman parameter was calculated, and the constitutive equation has been derived. Optimum parameters for the hot deformation were evolved avoiding the unstable metal flow regimes of 673–760 K at 0.1 to 1 s−1. Maximum power efficiency in the dynamic recrystallization domain of the alloy is found to be ∼0.6, indicating stable material flow during hot deformation. Strain rate sensitivity (m) value of 0.25–0.35 is observed in the stable regime at strain rates of 0.01–0.1 from 698 to 748 K indicating superplastic flow domain. Very fine recrystallized grains can be seen at higher temperatures greater than 723 K and lower strain rates of 0.1 and 0.01 s−1, which grow further with an increase in temperature, indicating onset of grain growth.

The valence electron structure analysis on the influence of hydrogen solid solution to the thermoplasticity of α-Ti and β-Ti

The thermo-hydrogen (THP) of titanium can improve the thermoplasticity performance by increasing volume fraction of the plastic phase, promoting the movement of dislocations and reducing the flow stress. It can significantly reduce the difficulty of titanium alloy hot working. Most of the explainations on THP remain at the grain and phase scale and some researches at the electron scale are not clear enough, which cannot fully reveal the mechanism of hydrogen induced thermoplasticity of titanium. Empirical electron theory (EET) of solids and molecules was applied to analysis the changes of valence electron structures when H dissolved into different interstices of α-Ti or β-Ti. Through bond length diffrence method (BLD), the the number of covalent bonding electron pairs between Ti-Ti, the energy of the chemical bond and the lattice electron density between glide planes were calculated, it can be got that the obvious decrease of he number of covalent bonding electron pairs and the energy of the chemical bond between Ti-Ti, and the increase of the lattice electron density between glide planes are the essential reasons of hydrogen induced thermoplasticity of titanium.

Microstructure, Tensile Properties, and Hot-Working Characteristics of a Hot Isostatic-Pressed Powder Metallurgy Superalloy

A series of microstructure observation, tensile, and hot compression tests were conducted to investigate the variation of microstructure, tensile properties, and hot-working characteristics of a powder metallurgy (PM) superalloy with hot isostatic pressing (HIPing) temperature, to establish a basis for the parameter selection for PM superalloy preparation. The results show that the dendritic structure from the powder was not completely removed until the HIPing temperature is above the γ′ solvus; γ/γ′ eutectic formed when the powder particles were HIPed at 1533 K (1260 °C) or above. Prior particle boundaries (PPBs) were observed in alloys HIPed at 1513 K (1240 °C) and below; the PPB decoration is serious in alloys HIPed at 1483 K and 1513 K (1210 °C and 1240 °C), owing to melting and aggregation of the boride phase at the particle boundaries during HIPing; the PPBs were eliminated when the HIPing was done at 1533 K (1260 °C) or above. Tensile fracture mode of the alloy changes from inter-particle and transgranular mixed fracture to transgranular fracture with increasing HIPing temperature, which is in accordance with the change in precipitate distribution at the PPBs. The hot workability of alloy is poor for all combinations of HIPing/deformation conditions except for HIPing at sub-solvus temperature and deformation at low strain rates.

Dynamic recrystallization behavior and processing map of the Cu-Cr-Zr-Nd alloy.

Hot deformation behavior of the Cu–Cr–Zr–Nd alloy was studied by hot compressive tests in the temperature range of 650–950 °C and the strain rate range of 0.001–10 s−1 using Gleeble-1500D thermo-mechanical simulator. The results showed that the flow stress is strongly dependent on the deformation temperature and the strain rate. With the increase of temperature or the decrease of strain rate, the flow stress significantly decreases. Hot activation energy of the alloy is about 404.84 kJ/mol and the constitutive equation of the alloy based on the hyperbolic-sine equation was established. Based on the dynamic material model, the processing map was established to optimize the deformation parameters. The optimal processing parameters for the Cu–Cr–Zr–Nd alloy hot working are in the temperature range of 900–950 °C and strain rate range of 0.1–1 s−1. A full dynamic recrystallization structure with fine and homogeneous grain size can be obtained at optimal processing conditions. The microstructure of specimens deformed at different conditions was analyzed and connected with the processing map. The surface fracture was observed to identify instability conditions.

High temperature deformation and processing map of a NiTi intermetallic alloy

The deformation behavior of a 49.8 Ni-50.2 Ti (at pct) alloy was investigated using the hot compression test in the temperature range of 700 °C–1100 °C, and strain rate of 0.001 s−1 to 1 s−1. The hot tensile test of the alloy was also considered to assist explaining the related deformation mechanism within the same temperature range and the strain rate of 0.1 s−1. The processing map of the alloy was developed to evaluate the efficiency of hot deformation and to identify the instability regions of the flow. The peak efficiency of 24–28% was achieved at temperature range of 900 °C–1000 °C, and strain rates higher than 0.01 s−1 in the processing map. The hot ductility and the deformation efficiency of the alloy exhibit almost similar variation with temperature, showing maximum at temperature range of 900 °C–1000 °C and minimum at 700 °C and 1100 °C. Besides, the minimum hot ductility lies in the instability regions of the processing map. The peak efficiency of 28% and microstructural analysis suggests that dynamic recovery (DRV) can occur during hot working of the alloy. At strain rates higher than 0.1 s−1, the peak efficiency domain shifts from the temperature range of 850 °C–1000 °C to lower temperature range of 800 °C–950 °C which is desirable for hot working of the NiTi alloy. The regions of flow instability have been observed at high Z values and at low temperature of 700 °C and low strain rate of 0.001 s−1. Further instability region has been found at temperature of 1000 °C and strain rates higher than 1 s−1 and at temperature of 1100 °C and all range of strain rates.

Simulating microstructural evolution during the hot working of alloy 718

The simulation of microstructural evolution during the primary breakdown of production-sized alloy 718 ingots and billets by radial forging was accomplished in the laboratory via multiple-stroke axial compression testing of cylindrical specimens. The dwell or hold time between strokes was varied to simulate the deformation-time history for three different locations along the radial-forging work piece: lead-end, mid-length, and tail-end positions. The microstructural evolution varied with simulated work piece position. Static, rather than dynamic, recrystallization was responsible for the observed grain-size refinement, and its repetitive occurrence during consecutive dwell periods resulted in the maintenance of a fine-grain microstructure during multiple-stroke deformation sequences. For comparison, the total plastic strain was also applied in a single-stroke test. The single- and multiple-stroke techniques gave differing microstructural results, indicating that multiple-stroke testing is necessary in modeling microstructural evolution during primary breakdown.

Flow stress and microstructural evolution during hot working of alloy 22cr-13ni-5mn-0.3n austenitic stainless steel

The stress-strain behavior and the development of microstructure between 850 °C and 1150 °C in an austenitic stainless steel, 22Cr-13Ni-5Mn-0.3N, were investigated by uniaxial compression of cylindrical specimens at strain rates between 0.01 and 1 s-1 up to a strain of one. The measured (anisothermal) and corrected (isothermal) flow curves were distinctly different. The flow stress at moderate hot working temperatures, compared to a number of other austenitic alloys, was second only to that of alloy 718. Both static and dynamic recrystallization were observed. Recrystallization was sluggish in comparison to alloy 304L, apparently due to the presence of a fine Cr- and Nb-rich second-phase dispersion, identified as Z phase, which tended to pin the high-angle grain boundaries even at a high temperature of 1113 °C. Recrystallization may also be retarded by preferential res-toration through the competitive process of recovery, which is consistent with the relatively high stacking-fault energy for this alloy. It is concluded that this alloy must be hot worked at temperatures higher than usual for austenitic stainless steels in order to minimize flow stress and refine grain size.