Papers by Keyword: Thermomechanical Processing (TMP)

Abstract: The present study deals with the effect of pre-deformation technique of AA2519 alloy (Al–5.64Cu–0.33Mn–0.23Mg–0.15Zr–0.11Ti–0.09V–0.08Fe–0.01Si (wt. %)) under T8 tempers, on condition that intermediate strains are equal. After undergoing T87 by pre-stretching and peak ageing the alloy demonstrates the yield stress, ultimate tensile strength and elongation to failure of 425.4±2.4 MPa, 475±2.4 MPa, 12.1±0.4%, respectively. The 7% pre-straining by rolling leads to-5% decrease in yield stress, practically the same ultimate tensile strength and-20% decrease in ductility. This effect can be ascribed to more homogeneous distribution of dislocations which act as heterogeneous nucleation sites for the θ′-phase precipitation. In addition to precipitates of the Al–Cu family (θ′′ and θ′), Ω-phase plates on {111}_α habit plane was observed. The effect of pre-straining prior to ageing on the precipitation behavior and its relation with mechanical properties of the AA2519 is considered.

Abstract: Microstructure, precipitation behaviour and mechanical properties of an Al-5.64Cu-0.33Mn-0.23Mg-0.14Zr-0.11Ti (in wt. %) alloy subjected to thermomechanical processing (TMP) involving equal-channel angular pressing (ECAP) at ambient temperature to total strains (ε) of ~1 and ~2 followed by aging at 180°C for 0-28 h have been investigated and compared with conventional aging at the same temperature (T6 state). TMP led to significant increase in yield stress (YS) and ultimate tensile strength (UTS) and decrease in elongation-to-fracture as compared to the peak-aged T6 state. The YS, UTS and δ values attained after ECAP to ε ~ 2 followed by peak ageing were ~510 MPa, ~540 MPa and ~7.6%, respectively. The changes in mechanical properties were related to microstructure evolution and precipitation behaviour. TMP conditions obtaining a high-strength state of the Al-Cu-Mg alloy are discussed.

Abstract: It is known that different parts of the gas turbine engine discs are operated at different temperature and load. Therefore, it is advisable to make such components out of nickel-based superalloys with a regulated structure that provides them the best operational properties. It is important to know the thermomechanical treatment for their processing to form such structures. Research of the deformation behavior and the microstructure evolution of nickel-based superalloys were carried out on small specimens. The accumulated strains and the stress distribution in specimens were determined during simulation. It is possible to predict structure formation on the basis of a deflected mode. Verification was carried out by isothermal upsetting of specimens out of superalloys at the temperature and strain rates determined by simulation. Thermomechanical treatments of the superalloys for different microstructure formation were defined. The features of the microstructure formation are shown depending on the chemical and phase composition of the alloys. Hot deformation of the ATI Allvac 718Plus superalloy leads to dissolution of the gamma prime phase that facilitates the deformation capacity. Increasing the alloyage of superalloys, including rhenium, leads to formation of a necklace structure instead of a homogeneous fine-grained structure for less alloyed superalloys at the same strain.

Abstract: Superplastic sheet metal forming allows the production of complex parts that are not formable under normal conditions. Superplastic sheet metal forming processes are normally based on the same common principle: the sheet metal is firmly clamped between the die halves and is blow-formed by means of gas pressure. Generally superplastic forming can only be achieved in a very narrow range of strain rates and temperature. Superplastic materials are relatively stable when deformed; this behavior is related to the observation that the flow stress of a superplastic material is very sensitive to the rate of deformation. This paper aims to study the formability characteristic of Magnesium alloy by considering variable parameters, such as the sheet thickness, forming pressure and forming temperature. The forming time of 120 minutes is constant for the formability test. Keywards: Multi dome test, superplasticity, Mg – alloy, Thermomechanical processing, Formability.

Abstract: The work focuses on the analysis of microstructural features of retained austenite in a thermomechanically processed Si-Al TRIP-type steel microalloyed with Nb and Ti. Austenite amount was determined using XRD and EBSD. Combined methods of LM, SEM and EBSD were applied to reveal the morphology, grain size and distribution of structural constituents. It is possible to retain 14% of  phase enriched in C to about 1.14 wt.%. Retained austenite is uniformly located as blocky grains with a diameter up to 4.5 m in a fine-grained ferritic matrix or between bainitic ferrite laths as thin layers. Special crystallographic relationships between bainitic ferrite and retained austenite were identified on the basis of the analysis of misorientation angles and image quality values.

Abstract: The history of Thixomolding®, its technology and commercialization are reviewed along with recent evolution of new technology afforded by its metallurgical structure. Since Thixomolding was introduced in the early 1990’s, it has developed to more than 400 Thixomolding machines in the United States, Canada, Japan, China, Taiwan, Hong Kong, Malaysia, Korea, Germany, Belgium and France. Applications have been established in the electronics/communication, automobile, military, hand tool, medical and sporting goods markets. Thixomoldings principal advantages are in net-shaping, consolidation of parts, safety, environmental friendliness, mechanical properties and microstructure. The virtuous isotropic and fine-grained Thixomolded® microstructure has opened the door to derivative thermal mechanical processing for generating nanostructured Mg products of high strength/density along with improved ductility, fatigue strength, corrosion resistance and formability. This thermomechanical processing (TTMP) has been applied recently to the Thixomolded precursor to further refine the grain size and eutectic phases to nanometer sizes - providing yield strength above 300 MPa, fatigue strength of 150 MPa along with elongation of >10%. Alloys so processed include AZ50L, AZ60L, AM60, AZ61L, AZ70L-TH, AZ80, AZ91D, AXJ810-TH and Thixoblended® alloys of higher Zn content. Microstructure is related to processing and properties, as predestined by the Thixomolded microstructure. Fiber Metal Laminate composites based on this nanoMAG TTMP Mg product have demonstrated yield strength up to 900 MPa, with modulus of elasticity of 90 GPa.

Abstract: The high temperature deformation behaviour of near alpha titanium alloy IMI834 with a bimodal microstructure has been evaluated by carrying out isothermal compression tests over a range of temperature and strain rate. The optimum thermomechanical processing (TMP) parameters i.e., temperature, strain rate that can be used to produce various aeroengine components were identified using dynamic materials modeling (DMM). Using kinetic analysis, a unified constitutive equation that describes the deformation behavior of the material in the selected temperature - strain rate regime has been established and the deformation mechanisms operating in the material were identified.

Abstract: Metastable beta-titanium alloys combine exceptionally low Young's modulus and high biocompatibility, thus attracting special interest in the prospect of their application as biomedical implant material. In this work, Ti-21.8Nb-6Zr (at.%) ingots were manufactured by vacuum argon melting followed by hot isothermal pressing. The obtained ingots were thermomechanically processed using the following TMP sequence: a) cold rolling (CR) from e=0.37 to 2 of the logarithmic thickness reduction; and b) post-deformation annealing (PDA) of between 450 and 700°C (10’…5 h for 600°C and 1 h for other temperatures). The influence of the TMP on the alloy’s mechanical properties under static and cyclic loading was studied.

Abstract: An experimental steel containing in weight % 0.2C-2.0Mn-1.5Si-0.6Cr has been laboratory hot rolled, direct quenched into the M_s - M_f range and partitioning annealed in order to explore new possibilities for making 1100 MPa yield strength structural steels with better combinations of strength, ductility and impact toughness. Two austenite states prior to quenching were investigated: recrystallized and strained. Gleeble simulations were used to determine appropriate cooling rates and cooling stop temperatures for obtaining martensite fractions in the range 70-90%. Desired martensite - austenite microstructures were achieved, and ductility and impact toughness were better than those obtained via the simple direct quenching of a lower carbon steel in the same strength class.

Abstract: A mathematical model was developed predicting the effects of alloying and thermomechanical processing on the final microstructure of steel. Various factors influencing transformation kinetics, including microalloying with Nb and plastic deformation of austenite, are considered. Subsequent stages of the model development and calibration are described.