Mechanical Thermal Treatment Research Articles

Microstructural Evolutions of a High Temperature Titanium Alloy Processed by Thermal Mechanical Treatments

TG6 alloy is a new titanium alloy which has been designed to reach the service temperature of 600°C. The microstructural evolutions of TG6 alloy under different thermal mechanical treatments were studied. It was found that lamellar microstructures with basketweave α lamella are obtained for TG6 alloy forged in β field. The evolution mechanism is transformed from dynamic recrystallization to dynamic recovery and the thickness of α lamella increases with increasing forging temperature. The aspect ratio of α lamella decreases firstly and then increases with increasing deformation degree. Grain boundary α lath appears when the deformation degree is less than 40%. The thermal mechanical treatments, including deformation in β field firstly and then deformation in α+β field result in the transformations of the microstructures drastically. The deformation degree in α+β field decides the final microstructure. The deformation degree of 20% in α+β field results in partial globular α phase.

Loading Surface in the Course of Mechanical-Thermal Treatment and Steady-State Creep of Metals

Loading Surface in the Course of Mechanical-Thermal Treatment and Steady-State Creep of Metals

Effect of Thermal-Mechanical Treatment on Texture and Properties of Cold-Drawn Steel Wire

Thermal–mechanical treatment is widely utilized by steelmakers to optimize the properties of high–strength cold drawing eutectoid steel wires. This paper presents the influence of industrial thermal–mechanical treatment utilized in practical manufacturing on microstructure and mechanical properties of drawn pearlitic steels. After post thermal–mechanical processing, drawn pearlitic steel features lower residual stress and improved yield/ultimate tensile strengths, and exhibits a more perfect fiber texture characteristic. Nevertheless, the torsion test of treated steel wire demonstrates that delamination occurs during torsional deformation, which implicates that the studied thermal–mechanical treatment is whereas not the optimum process for manufacturing the high–performance steel wires. The sequential TEM observation shows the remarkable different structure of pearlite lamellae in drawn and treated wires. The local stress concentration resulting from the separately granular cementite precipitation may attribute to the delamination of steel wire after post drawing.

Influence of sequence of cold working and aging treatment on mechanical behaviour of 6061 aluminum alloy

The influence of combination of different designated precipitation hardening and cold working on the tensile properties of 6061 aluminum alloy was investigated. The results indicate that applying single aging at 180°C for 4 h in different thermal-mechanical treatments improves both the strength and elongation. However, double aging does not improve the mechanical properties. In addition, pre-aging shows a negative effect on the subsequent precipitation hardening of material. The changes in mechanical properties were discussed by explanation of microstructural evolution due to the competition of precipitation hardening, strain hardening and work softening processes.

Effect of Zr element addition on the mechanical behavior of Ti48.5-xNi49.5Nb2 alloy

In this paper, quaternary Ti48.5-xNi49.5Nb2Zrx (x=0∼5at%) shape memory alloys were prepared by non-consumable vacuum arc melting. The microstructure and phase compositions of the shape memory alloys were investigated by scanning electron microscope and X-Ray Diffraction. The effects of Zr element and thermal mechanical heat treatments on the transformation temperature were studied by using differential scanning calorimetry. In addition, the mechanical properties of the alloys were tested. The results showed that the microstructure of ternary TiNiNb alloy was comprised of TiNi matrix and a Nb-enriched secondary phase. As for Zr element addition, when its content is lower than 3at.%, the Zr element was mainly dissolved in the TiNi matrix. When the content of Zr reaches 3at.%, a new secondary phase(Ti, Zr) 2Ni appeared and resulted in a degradation of workability. The martensite start temperature of the alloys decreased from 28.5°C to 16.1°C with the content of Zr element increasing from 0at.% to 5at.%. For Zr element increasing from 0at.% to 2at.%, the room temperature yielding strength of the alloys increased from 692MPa to 873MPa and the fracture strength increased from 472MPa to 578MPa.

EFFECTS OF THERMAL MECHANICAL TREATMENT ON THE MICROSTRUCTURES AND HARDNESS OF AN Al-Zn-Mg-Cu ALLOY PLATE

The effects of thermal mechanical treatment (TMT: solution-quenching-precipitation- rolling) on the morphology and the amount of the precipitates in an Al-7.81Zn-1.81Mg-1.62Cu alloy plate and the effects of those particles on the microstructures, textures and hardness have been studied. During TMT, MgZn2 particles with nano/submicron scales significantly inhibit the migration of sub- grain/grain boundaries but would not induce particle simulated nucleation (PSN) recrystallization. An appropriate TMT process results in the remarkable diminish of recrystallization and increases Vickers hardness by 15%.

Application of <i>Mikania micrantha</i> as an Additive of High Strength Eco-Materials

Mikania micrantha has invasive alien species harmful to many plants; it natively grows in South and Central America area. But now it is found throughout Asia and India area. It has a big reproductive capacity, so several researchers ever used thermal treatment, controlled-environmental treatment, mechanical treatment and biological control treatment to inhibit Mikania micrantha growth. However, rare studies use Mikania micrantha to make building materials. In this paper we will attempt to use untreated and treated (treated by carbonization) Mikania micrantha for making building bricks. Results are shown that the optimal uniaxial compressive strength occurred as 30 wt. % of the carbonized Mikania micrantha; the optimal uniaxial compressive strength took place as 40 wt. % of carbonized Mikania micrantha with an addition of organic acid. But the fresh Mikania micrantha has a lower uniaxial compressive strength, so we used interpolation method to calculate the optimized mixing ratio would be 5:95 for the fresh Mikania micrantha. In addition, Mikania micrantha as building material has no biotoxicity for E. coli.

Fe-6.5wt.%Si High Silicon Steel Sheets Produced by Cold Rolling

High silicon steel with Si content of 6.5wt.% is perspective to be applied in magnetic devices at high frequencies. It is very hard to produce Fe-6.5wt%Si alloy thin sheet by conventional hot-cold rolling method because of its embrittlement at room temperature resulted from the formation of intermetallic phases like B2 and D03. In this paper, embrittlement mechanism, rolling processes, and magnetic properties for the cold rolled Fe-6.5wt.% Si alloy sheets are discussed. Our study indicates that thermal mechanical treatments can improve the ductility of the Fe-6.5wt.%Si alloy. The Fe-6.5wt.%Si alloy sheets of 0.05 mm thickness can be successfully obtained after hot-cold rolling and heat treatments. Lamination pieces can be punched directly from the sheets. Tensile strength as high as 1048MPa and elongation over 3% were measured at room temperature.

Optimization of Microstructure and Elimination of β(B2) Phase in As-Cast Ti-Al-Nb-W-B Alloy

Abstract The microstructures of as-cast Ti-Al-Nb-W-B alloy were investigated to assess the possibility of eliminating the triaxial β(B2) phase on the crystal boundary through heat treatment and multi-step forging thermal mechanical treatment. The microstructure evolution and growth mechanism were studied according to Ti-Al-Nb ternary phase diagram, and then the process of eliminating of the triaxial β(B2) phase on the crystal boundary was assessed. The results of the experiments indicate that the best way to eliminate β(B2) phase is holding at the 1260 °C for 8 h or 1220 °C for 36 h followed by furnace cooling, but the grains grow appreciably. On the other hand, after multi-step forging with a total deformation of more than 80%, the as-cast nearly lamellar structure can be refined obviously to the duplex microstructure, and the β(B2) phase is basically eliminated.

EVOLUTION OF MICROSTRUCTURE AND MECHANICAL PROPERTIES OF THE Ni-25Al-27.5Fe-1.0Nb INTERMETALLIC ALLOY AFTER THERMAL MECHANICAL TREATMENT

The evolution of microstructure and mechanical properties of the Ni -25 Al -27.5 Fe -1.0 Nb intermetallic alloy after thermal mechanical treatment (TMT) was systematically investigated by means of X-ray diffractometry (XRD), scanning electron microscopy (SEM) with electron dispersive spectrum (EDS) capability, and atmosphere-controlled tensile test at room temperature with different strain rate. The results of XRD reveals that a matrix of β' phase [( Ni , Fe ) Al type ordered bcc structure] and a precipitated γ phase ( Ni 3 Fe fcc solid solution) co-exist in this alloy after TMT. The dendritic microstructure of the as-cast alloy was eliminated after TMT process. In parallel, a refined and homogeneous distributed lath precipitates can be obtained after annealing at 820 for 4 hr. Additionally, this alloy presents a relative high strength as well as ductile mechanical behavior (UTS~1320 MPa and ε~8%, respectively) at room temperature in air. A 30% improvement in yield strength is suggested to be contributed by the refined microstructure from the TMT. Moreover, the tensile strength and ductility of this alloy exhibit insensitive response with respect to the loading strain rate at room temperature.

Internal friction and impact toughness of structural BCC alloys

The paper deals with acoustic properties (Young's modulus E and logarithmic decrement δ) and impact toughness of the BCC alloys: low activation ferritic–martensitic steel EK-181 (produced in the RF) and V–(4–10)Ti–(4–5)Cr alloys (produced in the RF, USA and Japan). The materials have been investigated in ∼77–300 K temperature range where BCC metals usually become brittle at low temperatures. The acoustic measurements were made by composite oscillator technique mainly in the amplitude-independent damping ( δ i ) range at frequencies of longitudinal vibrations of about 100 kHz. The data have been obtained for annealed, plastically bent and bent-then-straightened specimens. The δ i ( T) dependences for the pre-bent samples show a similar behavior as the impact toughness of the alloys. So, the ductile to brittle transition temperature (DBTT) for the BCC alloys can be determined by an acoustic non-destructive technique. It has been found that the acoustical DBTT depends on microstructure of specimens (internal stresses) and is different for the EK-181 steel of different thermal–mechanical treatments and for the RF, USA and Japan vanadium alloys. A comparison of the δ i ( T) curves for the BCC EK-181 steel and for the FCC austenitic EK-164 steel is shown and discussed as well. A viscous dragging of edge dislocations is found to control the ductile to brittle transition of the BCC alloys.

Strength and fatigue properties enhancement in ultrafine-grained Ti produced by severe plastic deformation.

Severe plastic deformation (SPD) of titanium creates an ultrafine-grained (UFG) microstructure which results in significantly enhanced mechanical properties, including increasing the high cycle fatigue strength. This work addresses the challenge of maintaining the high level of properties as SPD processing techniques are evolved from methods suitable for producing laboratory scale samples to methods suitable for commercial scale production of titanium semi-products. Various ways to optimize the strength and fatigue endurance limit in long-length Grade 4 titanium rod processed by equal channel angular pressing (ECAP) with subsequent thermal mechanical treatments are considered in this paper. Low-temperature annealing of rods is found to increase the fatigue limit, simultaneously enhancing UFG titanium strength and ductility. The UFG structure in titanium provides an optimum combination of properties when its microstructure includes mostly equiaxed grains with high-angle boundaries, the volume fraction of which is no less than 50%.

The influence of preliminary mechanical-thermal treatment on the plastic and creep deformation of turbine disks

The influence of preliminary repeated mechanical thermal treatment on the strength of turbine disks has been studied. The analytical description in terms of a generalized synthetic theory has been carried out. The agreement between calculated and experimental data makes possible the use of the obtained results on an industrial scale.

Structural Characteristics and Anticorrosive Properties of a Titanium Bioalloy

In this paper, different thermal-mechanical treatments were applied on Ti6Al4V alloy and structural characteristics were correlated with anticorrosive properties in Ringer-Brown solution. Alloys present self-passivation with more electropositive corrosion potentials than of titanium; all electrochemical parameters have improved values, resulting the beneficial effect of the thermal treatment. Both alloys and base metal are very resistant in Ringer-Brown solution. Metallographic studies show that the thermal-mechanical treatments increased the corrosion resistance of the alloys in physiological fluids.

The manufacture of superplastic Magnesium alloy sheet

AbstractProbably because of their propensity to dynamically recrystallise, superplastic behaviour can be obtained from magnesium alloys considerably more easily than from comparable aluminium alloys. In some cases even as cast magnesium alloys can exhibit reasonable superplasticity and there appears no need for the special alloying additions or complex thermal mechanical treatments required by aluminium alloys such as AA2004 or AA7475. The paper describes the superplastic behaviour (in uniaxial tension) and microstructure of sheet processed from strip cast AZ31 and AZ91. The material was tested in the as‐cast condition and after warm rolling to a number of gauges. Industrially useful superplastic capability was demonstrated in strip cast AZ31 and AZ91 in the as cast condition. Furthermore good superplastic capability was also demonstrated in sheet rolled from the cast metal and the ductilities obtained were not significantly influenced by rolling strain. Twin roll strip casting represents a feasible and simple route for the production of superplastic material either for use in the as cast condition or after rolling to the required gauge.

The steel superstrengthening phenomenon, part 2

The paper discusses a combined heat treatment that includes the potentialities of high-temperature thermal-mechanical treatment and intensive quenching. Due to high-temperature thermal-mechanical treatment and intensive quenching within the martensite range, the strength and plastic properties of materials are significantly improved and compressive residual stresses are formed at the surface and small tensile stresses in the core, which result in the increase of their service life. The suggested combined approach is also efficient in the case of the heat treatment of forgings with the use of forging heat. The suggested technology considerably saves energy resources and makes unnecessary intermediate operations such as repeated heating before quenching. Oil, as a quenchant, is replaced by plain water. The industrial quenching line can be placed directly in the forgery workshop and yield big economical benefits.

Change of Young's Modulus of Cold-Deformed Aluminum AA 1050 and of AA 2024 (T65): A Comparative Study

The knowledge of some mechanical properties of materials and their changes with thermal treatments and/or mechanical treatments are essential to obtain the best results during simulation of processes. In this paper, changes of Young's modulus at room temperature of colddeformed aluminum AA1050 carried out in a tension machine and changes of Young’s modulus and Poisson’s ratio of AA2024 (T6 and T65) have been determined. The elastics constants have been measured by the ultrasound technique in AA2024 alloy and by tensile test in AA1050. In this alloy, the Young's modulus (E) diminishes during the first step of deformation and then increases with the successive cold working. Changes in Young's modulus measured are around 6-8%. In AA2024, the Young's modulus change is about 3% between the annealed and quenched alloy (minimum value); during aging the E parameter increases with respect to quenching. These changes are correlated with the structural changes during thermal treatments. In AA2024, the E parameter remains almost constant during cold-working after the aging treatment. Poisson’s ratio of this alloy remains almost constant in all the treatments. These results are also correlated with the dislocations arrangement in both materials. This behaviour is also compared with cold-deformed pure iron in a tensile test. These results confirm that aluminum AA1050 present similar behaviour than it was observed for pure iron.

Microstructure, texture and mechanical properties of continuous cast AA 5083 aluminium alloy

Continuous cast AA 5083 aluminium alloy hot band with and without prior heat treatment at 510°C for 3 h was cold rolled to a reduction of 70% and annealed at 399°C for 3 h. It was found that the alloy without the prior heat treatment showed a strong {113}〈110〉 texture component after the thermal mechanical treatment, while with the prior heat treatment its recrystallisation texture was almost random. The alloy with the prior heat treatment exhibited a fine equiaxed grain structure after annealing, in contrast to a coarse elongated one in the alloy without the prior heat treatment. The tensile properties and their isotropy of the alloy were greatly improved by the prior heat treatment. The concurrent precipitation effect was likely to be responsible for the formation of the new texture and inferior mechanical properties of the alloy. Precipitates of 20 nm in size were observed interacting with dislocations in this alloy.

Microstructure evolution during homogenization of a τ-type Mg–Zn–Al alloy

Microstructure evolution during homogenization of a low-alloying τ-type Mg–Zn–Al magnesium alloy with a nominal composition of Mg–7% Zn–3% Al was investigated in this paper, using optical microscopy, scanning electron microscopy, X-ray diffraction, differential scanning calorimetry analysis and quantitative image analysis. A anneal treatment following rapid cooling to ambient temperature from homogenization isothermal temperature was adopted to assess the homogenization degree in respect to microchemical distribution. The results show that shorter holding time results in so-called in situ precipitation phenomena, which is attributed to the insufficient diffusion of the element Zn and Al from solute-rich grain boundary region to inner side of grain during homogenization. A homogenization treatment at 325 °C for at least 50 h is just enough allowing complete homogenization for such alloy, in point of both morphology and microchemistry of the microstructure, which is deemed to be a key precondition for the optimum combined properties through proper thermal–mechanical treatment.

Gas phase embrittlement and time dependent cracking of nickel based superalloys

Nickel based superalloys are critical to the safe operation of many energy conversion systems operating at high temperatures. Time dependent intergranular cracking of these alloys, under both sustained and cyclic loads, is dominated by environmental interactions at the crack tip. This review is concerned mainly with the interaction of oxygen in alloys used for combustion turbine discs, although interactions with other more aggressive species are considered. The phenomenology of this cracking is shown to be consistent with the same mechanism as that associated with oxygen embrittlement resulting from pre-exposure of uncracked material, and also with environmentally induced reduction in creep rupture life. Gas phase embrittlement (GPE), resulting from intergranular oxygen penetration, is shown to be responsible for all four streams of experimental observations. Three distinct processes of intergranular embrittlement involving oxidation reactions have been confirmed experimentally. One of these, the oxidation of intergranular sulphides, results in elemental sulphur embrittlement and subsequent local decohesion under stress. The other two, oxidation of carbon or carbides to form carbon dioxide gas bubbles and oxidation of strong oxide formers to form intergranular internal oxides, result in a reduction of the local ability to accommodate stress concentrations associated with sliding grain boundaries in an intermediate temperature range. This in turn leads to a temperature dependent minimum in ductility and maximum in crack propagation rate. Attempts to reduce the sensitivity to time dependent cracking based on chemistry (chromium level or trace element addition), microstructure control (using thermal–mechanical treatment or controlled cooling), or reversal of environmental embrittlement, are all considered. The conclusions form a basis for the development of life prediction methods for energy materials operating in diverse environments.