Papers by Keyword: Hot Deformation

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Authors: Rustam Kaibyshev, Oleg Sitdikov, Alexandre Goloborodko, Taku Sakai
Authors: Ting Li, Kui Zhang, Zhi Wei Du, Jia Wei Yuan, Xing Gang Li
Abstract: The hot deformation behavior of Mg-7Gd-5Y-1Nd-0.5Zr alloy was investigated by compression tests at temperatures of 673 K, 713 K, 753 K, and 793 K and strain rates of 0.001 s-1, 0.01 s-1, 0.1 s-1, and 1s-1. The stress-strain curves exhibit typical dynamic recrystallization behavior with a single peak stress followed by a gradual fall toward a steady-state stress. The apparent activation energy of deformation and constitutive equations for the alloy were determined through regression analysis for conventional hyperbolic sine equation. The apparent activation energy of DRX and dynamic kinetics model for alloy were determined using the regression analysis for Avrami equation. Optical microscope and electron backscattered diffraction were employed to investigate the microstructure evolution of Mg-7Gd-5Y-1Nd-0.5Zr alloy during hot compression. The results suggested that the grain boundary is the main nucleation sites of dynamic recrystallization, and (0001) basal fiber texture has formed during hot compression.
Authors: Tara Chandra, Jose María Cabrera, Jose Manuel Prado
Authors: Jing Qi Zhang, Hong Shuang Di, Xiao Yu Wang
Abstract: In the present study, deformation heating generated by plastic deformation and its effect on the processing maps of Ti-15-3 titanium alloy were investigated. For this purpose, hot compression tests were performed on a Gleeble-3800 thermo-mechanical simulator in the temperature range of 850-1150 °C and strain rate range of 0.001-10 s1. The temperature rise due to deformation heating was calculated and the as-measured flow curves were corrected for deformation heating. Using the as-measured and corrected flow stress data, the processing maps for Ti-15-3 titanium alloy at a strain of 0.5 were developed on the basis Murty‘s and Babu’s instability criteria. The results show that both the instability maps based the two instability criteria are essentially similar and are characterized by an unstable region occurring at strain rates higher than 0.1 s1 for almost the entire temperature range tested. The unstable regions are overestimated from the as-measured data due to the effect of deformation heating, indicating a better workability after correcting the effect of deformation heating. This is further conformed by the analysis based on strain rate sensitivity.
Authors: Gang Wang, Chun Yan Wang, Zhe Chen, Wen Ru Zhao, Yan Dong Liu, Yan Dong Wang, Liang Zuo
Abstract: NiMnCoIn alloys are new-type magnetic shape memory alloys (MSMAs) in which a reversible magnetic-field-induced phase transformation was observed. They are ideal candidates of materials used in actuators and sensors. The polycrystalline NiMnCoIn alloys are generally brittle so that they can not be easily deformed into the shape applicable to actuators and sensors until now. In the present paper, the influence of hot deformation on the microstructure of Ni45Co5 Mn36.7In13.3 alloy was studied. The experimental results showed that second phase was observed after deformation at high temperature between 800~900 °C and at strain rate lower than 4×10-3s-1. The content of Co of second phase was higher than the matrix alloy, while the content of In was lower than the matrix alloy. It was determined by TEM measurements as γ phase with fcc structure which was popular in NiFeGa and NiMnGaCo alloys. It is possible to improve the ductility of Ni45Co5Mn36.7In13.3 alloy by control of amount and distribution of γ phase by hot deformation.
Authors: P.S. Robi, Sanjib Banerjee, A. Srinivasan
Abstract: High temperature deformation behavior of Al–5.9%Cu–0.5%Mg alloy and Al–5.9%Cu–0.5%Mg alloy containing 0.06 wt.% of Sn was studied by hot compression tests at various temperatures and strain rates. Addition of trace amounts of Sn into the Al–Cu–Mg alloy system resulted in a significant increase of flow stress for all conditions of temperature and strain rate. 100% and 89% of the flow stress values during hot deformation could be predicted within ± 10% deviation values for the aluminum alloys with and without Sn content, respectively, by artificial neural network (ANN) modeling. From the deformation mechanism maps and microstructural investigation, the safe process regimes for hot working of the base alloy was identified to be at (i) very low strain rate (< 0.003 s−1) at temperature < 450 °C, and (ii) high temperature (> 400 °C) with strain rate > 0.02 s−1. For the micro-alloyed alloy, it was at low strain rates (< 0.01 s-1) for the entire temperature range studied. Flow softening for both alloys was observed to be at low strain rates and was identified to be due to dynamic recrystallization (DRX). The metallurgical instability during deformation was identified due to shear band formation and/or inter-crystalline cracking.
Authors: Atef S. Hamada, L. Pentti Karjalainen, Mahesh C. Somani, R.M. Ramadan
Abstract: The hot deformation behaviour of two high-Mn (23-24 wt-%) TWIP steels containing 6 and 8 wt-% Al with the fully austenitic and duplex microstructures, respectively, has been investigated at temperatures of 900-1100°C. In addition, tensile properties were determined over the temperature range from -80 to 100°C. It was observed that in spite of the lower Al content, the austenitic steel possessed the hot deformation resistance about twice as high as that of the duplex steel. Whereas the flow stress curves of the austenitic steel exhibited work hardening followed by slight softening due to dynamic recrystallisation, the duplex steel showed the absence of work hardening and discontinuous yielding under similar conditions. Tensile tests at low temperatures revealed that the austenitic grade had a lower yield strength than that of the duplex grade, but much better ductility, the elongation increasing with decreasing temperature, contrary to that for the duplex steel. This can be attributed to the intense mechanical twinning in the austenitic steel, while in the duplex steel, twinning occurred in the ferrite only and the austenite showed dislocation glide.
Authors: Apichat Sanrutsadakorn, Vitoon Uthaisangsuk, Surasak Suranuntchai
Abstract: In this work, two approaches for determining critical stress and strain for initiation of dynamic recrystallization (DRX) of the AISI 4340 steel were presented.The first one applied a polynomial function to represent relationship between work hardening rate and flow stress. Secondly, Cingara constitutive model were employed. To investigate hot deformation behavior of the steel, compression tests were performed at different temperatures between 850 °C and 1150 °C and strain rates between 0.01s-1and 10 s-1. Obviously, both methods provided different values of critical stress and critical strain.Accuracy of the first method depended on fluctuations of the fitted strain hardening curve. On the other hand, results of the Cingara model was primarily related to the described flow curves up to their peak points. It could be noticed that the DRX occured during hot deformation of the examined steel started when the normalized critical stress and strain reached the values of 0.735 and 0.324, respectively.
Authors: Kuldeep Kumar Saxena, Vivek Pancholi, Dinesh Srivastava, G.K. Dey, Sanjay K. Jha, Nudurupati Saibaba
Abstract: Hot workability of Zr-2.5Nb-0.5Cu alloy has been investigated by means of hot compression test using Gleeble-3800®, in the temperature and strain rate range of 700 to 925°C and 0.01-10s-1, respectively. Deformation behavior was characterized in terms of flow instability using peak stress with the help of Lyapunov Function. The true stress-strain curves shows that softening occurs at all lower temperature and for entire strain rates of deformation. The instable flow was suggested by negative m value at deformation condition of 700°C (5 and 10 s-1), while s value at 925°C (10 s-1). The combined result of rate of change of m and s with respect to log strain rate suggest that the deformation condition ranges from 725-780°C (10-2- 10-1 s-1) and 700°C (1-10 s-1) representing safe domain for stable flow.
Authors: Fernando Warchomicka, Cecilia Poletti, Martin Stockinger, Hans Peter Degischer
Abstract: Titanium alloys are attractive for structural applications in the aerospace industry due to their high specific strength in comparison with other engineering materials. These properties are strongly related to the microstructure obtained during thermo-mechanical processes. The influence of the processing parameters on the microstructure is investigated to determine criteria for the control of the forming processes. Pre-forged specimens of alpha-beta Ti-6Al-4V alloy with elongated primary alpha grains are deformed below the beta transus temperature between 0.1 and 10/s of strain rate. Compression is carried out parallel and perpendicular to the preferential orientations of the primary alpha grains. The local strain within the compressed samples is determined by finite element methods and correlated to the microstructure observed there. The alpha content is affected by the temperature of deformation and the morphology of the alpha grains is influenced by the strain and strain rate. Specimens with previous primary alpha grains parallel to the compression axis show a rotation of the alpha grains which were oriented almost perpendicular to the load axis. EBSD measurements are used to determine the restoration mechanism involved during hot deformation. Continuous dynamic recrystallization in the alpha grains is revealed by increasing the cumulative crystallographic misorientation towards the grain boundary and the formation of new grains. This misorientation increases with increasing values of the Zener Hollomon parameter (Z). For lower values of Z restoration occurs mainly in the beta phase.
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