Short Duration Heat Treatment Research Articles

Effects of a short-duration preprecipitation process prior to predeformation aging on the mechanical properties and corrosion resistance of Al-Cu-Mg-Ag alloy

PurposeThe effects of the thermo-mechanical treatment on the properties and microstructure of the Al–Cu–Mg–Ag alloy were investigated.Design/methodology/approachA short-duration preprecipitation process is designed prior to predeformation aging. The novel predeformation aging (solution treatment + holding at 185 °C for 15 min+ rolling deformation + aging at 185 °C, also named T8) was performed on a heat-resistant Al–Cu–Mg–Ag alloy.FindingsThe purpose of this study indicate that a short-duration heat treatment before predeformation is beneficial to the precipitation of O during the aging process. The precursors of O during this process might pin the dislocation and cause the grains to orient along some specific direction, which might be advantageous to the precipitation of O while disadvantageous to that of θ′. This novel thermal-mechanical process could result in an increase in the quantity and decrease in the size of the precipitation of O, which leads to a remarkable strength effect. The potential increases while the current density decreases with an increase in the deformation amount, which implies a smaller intergranular corrosion rate. The fine deformed structure leads to an opposite behavior in the exfoliation corrosion test compared with that for intergranular corrosion.Originality/valueThe intergranular corrosion resistance of the Al–Cu–Mg–Ag alloy is enhanced, whereas the exfoliation corrosion resistance is reduced by novel predeformation aging.

Short Duration Heat Treatments before Aging Increase Mechanical Hysteresis of Pseudoelastic NiTi Alloy

High temperature (550 °C) and short duration (10, 15, 20 s) heat treatments were performed on pseudoelastic NiTi alloy in addition to the conventional aging process in order to increase the mechanical hysteresis of the material. Pre-treated and aged samples were compared with plain aged ones through mechanical testing, powder X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The introduction of the pre-treatment, in combination with the aging process, was shown to increase the mechanical hysteresis of the aged samples up to ~30% after stabilization. XRD analysis showed how the introduction of the pre-treatment introduces a recovery of the residual stresses in the material microstructure, as well as the nucleation of different sets of metastable precipitates (such as TiNi3). We thus observe that the combination of pre-treatment and aging affects the alloys microstructure, causing a series of effects that synergise in increasing the material hysteresis.

Friction stir extrusion of ultra-thin wall biodegradable magnesium alloy tubes — Microstructure and corrosion response

Magnesium alloys are increasingly being considered for structural systems across different industrial sectors, including precision components of biomedical devices owing to their high specific strength and stiffness, biodegradability. For example, tubular devices such as coronary stents manufacture require defect-free, high-quality tubes with thin walls (100 μm – 1 mm) as a precursor. Here, we have produced fully consolidated, structurally sound ultra-thin walled (∼ 400 μm) AZ31 Mg alloy tubes by friction stir back extrusion (FSE) — a relatively new severe deformation process used typically to manufacture thick metallic tubes and rods. The tube cross-sectional microstructure was layered and consisted of a severely deformed stir zone with refined grains near the inner edge, a back-extruded zone with small grains near the outer edge, and a thermomechanically affected zone (TMAZ) with coarse grains develop within the central region. On the other hand, the inner tube surface microstructure had an average grain size of 4.1 ± 1.9 μm and a strong basal texture. In comparison, the outer tube surface microstructure was coarse, with an average grain size of 13.3 ± 6.4 μm with no preferred orientation. The microhardness variation along the tube wall thickness indicated the operation of multiple deformation paths during FSE. Upon exposure to Hank’s balanced salt solution at 37 °C, microgalvanic coupling resulting from the gradient through-the-thickness grain size and texture differences between the tube inner and outer surfaces, and residual strain arising from the FSE process, promoted a localized attack that preferentially initiated on the outer tube surface and progressed inwards. Static recovery induced by a short duration heat treatment at low temperature did not alter the microstructure but promoted a more general corrosion attack with a significantly reduced corrosion rate. Our results establish that FSE is a viable single-step process to manufacture ultra-thin Mg alloy tubes suitable for degradable precision tubular applications.

Microstructural modification and ageing behaviour of the Al–17Si–5Cu alloy using a novel approach

ABSTRACTA novel short duration heat treatment schedule is proposed in the present investigation for the Al-17 wt-% Si-5 wt-% Cu alloy (AR alloy). The existing heat treatment uses long duration (4–24 h) holding at solutionising temperature prior to ageing treatment. In the present investigation, the AR alloy is subjected to isothermal holding at 590°C for 15 min followed by warm water quenching prior to the normal ageing schedule. Detailed microstructural investigations involving size and shape of primary as well as eutectic Si particles, porosity measurements along with hardness and tensile property characterisation are carried out to find the effect of isothermal heat treatment. The study reveals considerable improvement in microstructure and mechanical properties after this isothermal heat treatment.

Enhanced elevated temperature wear resistance of Al−17Si−5Cu alloy after a novel short duration heat treatment

The goal of the present study is to improve the elevated temperature wear resistance of an Al−17wt%Si−5wt%Cu alloy (AR alloy) by a novel short duration heat treatment process. The elevated temperature (100°C) dry sliding wear behavior of an AR alloy was studied after microstructural modification using the proposed heat treatment. The study revealed considerable microstructural modifications after the heat treatment and the heat treated alloy was designated as HT (heat treatment) alloy. A higher hardness value was obtained for the HT alloy compared to the AR alloy. Accordingly, the wear rate for the HT alloy was found to be significantly lower compared to the as-cast AR alloy at all applied loads. Accelerated particle pull-out for the AR alloy at elevated temperatures resulted in poor wear behavior for it compared to the HT alloy. On the other hand, the Si particles remained intact on the worn surface of the HT alloy due to the good particle/matrix bonding that resulted from the isothermal heat treatment. Furthermore, the age hardening that occurred in the HT alloy during wear provided additional wear resistance. Thus, the HT alloy at 100°C exhibited a lower wear rate compared to the AR alloy even at room temperature for all applied loads. This improvement was attributed to microstructural modification upon isothermal heat treatment along with the age hardening effect.

Microstructure mapping of a friction stir welded AA2050 Al–Li–Cu in the T8 state

The heterogeneous precipitate microstructure of a AA2050 Al–Li–Cu in the T8 state after friction stir welding has been mapped by small-angle X-ray scattering (SAXS). 2D resolved maps of the fraction and size of both T1 platelets precipitates and clusters/GP zones formed at room temperature are provided. TEM micrographs of selected zone confirm the interpretation of SAXS intensities. This microstructure mapping is compared to microhardness mapping and a direct correlation is shown. Short duration heat treatments made in a salt bath help understanding precipitate stability and suggest that the temperature exploration alone explains to a large extent the distribution of the precipitates microstructure across the welded structure.

EBSD Coupled to SEM <i>In Situ</i> Annealing as a Tool to Identify Recrystallization Mechanisms - Application to Zr and Ta Alloys

A heating stage as been developed to performin-situannealing in a SEM equipped with an EBSD system in order to study recrystallization mechanisms. High temperature treatments could then be performed inside the SEM, up to 1180°C and with high heating-and cooling-rates (~100°C.s-1). Samples were cooled down to room temperature to perform EBSD orientation mapping in between successive short-duration heat-treatments. Microstructure evolution snapshots obtained this way are presented in this paper to show recrystallization in Zircaloy4 and in pure tantalum.

Influence of heat treatments at 475 and 400 °C on the pitting corrosion resistance and sensitization of UNS S32750 and UNS S32760 superduplex stainless steels

AbstractSome precipitation reactions of superduplex stainless steels (SDSS) can improve hardness, yield, and ultimate strength, but with substantial decrease of corrosion resistance. One of these reactions is the spinodal decomposition of ferrite into Cr‐rich fine precipitates (α′) and Cr‐depleted matrix during low temperature aging. In this work, the effect of the α′ precipitation on the pitting corrosion resistance was investigated. The results showed that short duration heat treatments at 475 °C do not decrease the pitting corrosion resistance, but increase the hardness of UNS S32750 and S32760 SDSS. The limits of heat treatment duration for both steels were determined.

Study of short duration heat treatments of an in situ copper-sheathedMgB2 wire

The powder-in-tube technique has been used to fabricate Cu-sheathed magnesium diboride(MgB2) wiresusing an in situ reaction method. The effects of high heating rate, short duration heat treatments ofMgB2/Cu wires were studied by means of optical and scanning electron microscopy, x-ray diffraction, resistivity,ρ(T), andsusceptibility, χ′(T), measurements. The transport critical currents,Ic(B), of the wires were measured using both direct current in a constant field andpulse field–pulse current methods. Usage of high heating rates allows theprocesses of interest to occur in conditions closer to isothermal, which permitsthe influences of heat treatment time and temperature to be more readilydistinguished. The results show that the microstructure and properties of theMgB2/Cu wires are strongly dependent on the heat treatment temperature butquite insensitive to the reaction time: a short heat treatment for 5 min at700 °C was sufficient for obtaining the highest critical current achieved in this work.

Magnetoimpedance of a glass-coated amorphous microwire

A maximum magnetoimpedance (∼66%) was observed at 5.2 MHz in a positive magnetostrictive glass-coated amorphous Co83.2Mn7.6Si5.8B3.3 microwire. Giant magnetoimpedance in this microwire was increased to 129% on short-duration heat treatment by passing four current pulses of amplitude of 100 mA and each of 12 s duration. Magnetoimpedance of the as-quenched and heat treated microwires was investigated as a function of a dc magnetic field Hdc within ±120 Oe and frequency f up to 12.85 MHz. The magnetization measurements of the samples indicated that the increase in giant magnetoimpedance on short-duration annealing is due to the increase in outer shell volume of the domain structure.

A three step method for synthesis of HTSC Bi 2CaSr 2Cu 2O 8 + δ

A method for the preparation of high Tc superconductor (HTSC) Bi 2CaSr 2Cu 2O 8 + δ involving three steps has been adopted. Firstly two compositions namely Bi 2O 3 + CaO and SrCO 3 + CuO were prepared, these were then mixed in the molar ratio 1:2. Short duration heat treatment at temperature approaching melting stage, which here was well above 900°C due to pre-conversion of Bi 2O 3 into CaBi 2O 4, resulted in formation of material rich in the desired phase. Characterisation of samples by XRD, EMPA, electrical and magnetic methods has been done.

Effective Permeability due to High Temperature Annealing in Amorphous Alloy

The effect of heat treatment conditions on the high-frequency characteristics of amorphous materials was studied. In the range 300 kHz to 1 MHz, permeability reached a peak at a heat treatment time of around 100 min., about 20 percent higher than the permeability peak for short duration heat treatment. Permeability increased at 1 MHz for all heat treatment temperatures, peak time decreasing with increase in heat treatment temperature. It was confirmed that it is possible to have both a composition with T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> and T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> close to each other, and to use water quenching heat treatment.

Effect of isothermal exposure on fatigue crack growth in boron-titanium composites

Fatigue crack growth testing has been applied to boron/Ti-6Al-4V composites in order to investigate simultaneously crack propagation mechanisms during the fatigue and overload portion of the experiments. It is concluded that linear elastic fracture mechanics (LEFM) for heterogeneous and anisotropic materials facilitates understanding of the rupture mechanisms and the assessment of failure work and toughness. The influence of isothermal exposure on crack propagation mechanisms has been pointed out. A short duration heat treatment at 850‡ C improves the composite toughness and reduces the fatigue crack growth rate although the fibrematrix (FM) interfacial bonding is increased. This effect has been related to a damage mechanism initiated in the interfacial reaction zone. In any case, the fatigue behaviour of the composite is controlled by the matrix and the capability of the fibres to function as crack arrestors. The impeding effect of the fibres is no longer effective when the thermal exposure duration is significant.

Effect of hyperthermia on protein biosynthesis in L5178Y murine leukemic lymphoblasts.

AbstractThe effects of elevated temperatures upon protein biosynthesis were determined in L5178Y murine leukemic lymphoblasts. The rate of protein synthesis was inhibited proportionately to the increase in temperature. Efforts were made to determine the mechanism of heat inactivation of protein synthesis by studying the requirements for recovery of activity after the cells were returned to 37°C. The ability of actinomycin to block the recovery process suggests that elevated temperatures destroy or inactivate a species of RNA required for protein synthesis. Loss of RNA during heating of the cells is apparently at least partially dependent on protein synthesis, since the presence of cycloheximide during heat shock, is capable of ameliorating the effects of short duration heat treatment.