Texture dependent stress corrosion failure of commercial titanium sheets in bromine-methanol solution

The stress corrosion cracking (SCC) characteristics of -titanium sheets in a bromine-methanol solution have been studied in the annealed and cold-rolled conditions using longitudinal and transverse specimens. The times to failure for annealed longitudinal specimens were longer than those for similarly tested transverse specimens. The cold-rolled specimens developed resistance to SCC, but failed by cleavage when notched, unlike the intergranular separation in annealed titanium. The apparent activation energy was found to be texture dependent and was in the range 30 to 51 kJ mol^–1 for annealed titanium, and 15kJ mol^–1 for cold-rolled titanium. The dependence of SCC behaviour on the texture is related to the changes in the crack initiation times. These are caused by changes in the passivation and repassivation characteristics of the particular thickness plane. The thickness planes are identified with the help of X-ray pole figures obtained on annealed and cold-rolled material. On the basis of the activation energy and the electrochemical measurements, the mechanism of SCC in annealed titanium is identified to be the one involving stress-aided anodic dissolution. On the other hand, the results on the cold-rolled titanium are in support of the hydrogen embrittlement mechanism consisting of hydride precipitation. The cleavage planes identified from the texture data match with the reported habit planes for hydride formation.     

Bend ductility of 70-30 alpha brass

• 1.1. Bend ductility of cold-rolled specimens and specimens cold-rolled, partially recrystallized, and cold-rolled additionally 10–30% was determined.
• 2.2. Considerable improvement in bend ductility was obtained for a given Diamond Pyramid Hardness for the partially recrystallized and re-rolled specimens.

     

Texture modification of magnesium alloys during electropulse treatment

ABSTRACT

Differential speed rolling (DSR) at room temperature has been carried out on two Mg–1Gd and Mg–1Zn–1Gd rare-earth-containing magnesium alloys with different thickness reductions. The cold-rolled samples were selected to investigate the microstructure and texture evolution during the electropulse treatment (EPT). Both grain refinement and texture modification have been achieved for the three cold-rolled samples, which were accompanied by nucleation and nuclei growth during EPT. The recrystallisation process could be attributed to enhanced climb activity of dislocations by EPT, which produces not only a thermal effect but also an athermal effect. Compared with Mg–1Gd, Mg–1Zn–1Gd shows a smaller recrystallisation rate, which should be related to the solute segregation and could be one of the reasons for the texture modification of the alloy.

This paper is part of a themed issue on Materials in External Fields.     

The effect of heat-treatment and nitrogen addition on the critical current density of a worked niobium 44 wt % titanium superconducting alloy

Mechanical working of a single phase superconducting alloy leads to an increase in the critical current density,J _c, After cold-rollingJ _c exhibits anisotropy as the angle of the magnetic field to the rolled surface is changed. This paper studies the effects of interstitial addition and heat-treatment onJ _c and its anisotropy in both cold-rolled and wire-drawn alloy. The variations inJ _c are correlated with the observed changes in the microstructure.     

Rolling and annealing textures of a SiCw/Al composite

A SiC whisker reinforced pure aluminum composite (SiC_w/Al) was fabricated using a squeeze casting route and cold-rolled to 50% reduction in thickness. Some cold-rolled composites were then annealed at 500 °C for 1 h. The pure aluminum was also cold-rolled and annealed in the above way for comparison purpose. The textures of the cold-rolled and annealed materials were examined using XRD technique. It was found that the dominant texture components in the cold-rolled composites consisted of {112}〈111〉, {100}〈011〉 and {123}〈634〉. They were much weaker than those in the cold-rolled aluminum. When the cold-rolled composites were annealed, the new texture components {211}〈213〉, {013}〈131〉 and {011}〈211〉 occurred and had the similar intensity as the texture components remained from the deformation state. This indicated that the recovery reaction and recrystallization occurred simultaneously when the cold-rolled composite was annealed 1 h at 500 °C. Like the situation of the deformed materials, the annealing texture was also much weaker in the composite than in the aluminum. The weaker deformation and annealing textures in the composites can be attributed to the introduction of the whiskers.     

Annealing studies of cold-rolled Ni3Al

Annealing studies of cold-rolled Ni₃Al established that the recrystallization kinetics obey the Avrami equation and that the grain-growth kinetics obey the relation ¯d=Ct ⁿ where ¯d is the average grain size, t the time and C and n are parameters whose magnitude depends on temperature. Disorder is introduced during deformation but subsequently removed during recrystallization. Antiphase boundaries are found in some recrystallized grains but do not show any preference to lie on {100} planes, contrary to predictions based on Flinn's nearest-neighbour approximation model. Twins, dislocation networks an planar faults are also found in recrystallized grains.     

Influence of substitution of phenyl group by naphthyl in a diphenylthiourea molecule on corrosion inhibition of cold-rolled steel in 0.5 M H2SO4

N,N′-Diphenylthiourea (DPTU) and N-naphthyl-N′-phenylthiourea (NPTU) synthesized in our laboratory, were tested as inhibitors for the corrosion of cold-rolled steel in 0.5 M H₂SO₄ by weight loss and electrochemical measurements. The studies clearly reveal that when we substitutes a phenyl group in N,N′-diphenylthiourea (DPTU) by naphthyl group to obtain N-naphthyl-N′-phenylthiourea (NPTU), the inhibition efficiency increases from 80 to 96% at 2 × 10⁻⁴ M. Polarization curves show that NPTU acts as mixed type inhibitor whereas DPTU predominates as cathodic inhibitor. Changes in impedance parameters (charge transfer resistance, R _t, and double layer capacitance, C _dl) were indicative of adsorption of DPTU and NPTU on the metal surface, leading to the formation of protective films. The degree of the surface coverage of the adsorbed inhibitors is determined by ac impedance technique, and it was found that the adsorption of these inhibitors on the cold-rolled steel surface obeys the Langmuir adsorption isotherm. The effect of the temperature on the corrosion behavior with addition of 10⁻⁴ M of DPTU and NPTU was studied in the temperature range 20–50 °C. Results show that the rate of corrosion of mild steel increased with increasing temperature both in the presence of inhibitors and in their absence. Activation energies in the presence and absence of DPTU and NPTU were obtained by measuring the temperature dependence of the corrosion current. The reactivity of these compounds was analyzed through theoretical calculations based on density functional theory to explain the different efficiency of these compounds as corrosion inhibitors.     

Ferrite recrystallisation and intercritical annealing of cold-rolled low alloy medium carbon steel

Static recrystallisation of cold-rolled AISI 4130 medium carbon steel in the ferritic regime and its response to intercritical annealing treatment are studied. A fine and recrystallised microstructure with improved mechanical properties is obtained via subcritical annealing of cold-rolled sheet, where the subsequent intercritical annealing results in the enhancement of tensile strength via the formation of dual-phase microstructure. Intercritical annealing of the cold-rolled sheet is characterised by an initial drop in hardness due to recrystallisation and subsequent rise in hardness as a result of austenitisation. It is revealed that continuous martensite phase can result in a higher deformation resistance. Finally, the effects of intercritical annealing at temperatures below pearlite dissolution finish temperature (Ac_1f) are discussed.     

Druckversuch an Scheiben zur Prüfung der Wasserstoffversprödung von Metallen

Disc-Pressure-Testing of Hydrogen Embrittlement An apparatus for disc-pressure-tests is presented. The bursting pressure with helium and with hydrogen is measured versus the rate of pressure increase. Under hydrogen most metals show a distinct minimum of bursting pressure. Some explanations for this minimum are proposed. The maximum ratio of bursting pressures x = (P_He/H_H2)_max is taken as an indicator for hydrogen embrittlement. Steel similar to SAE 4137 (34 CrMo 4) is tested in several states (tempered, normalized, cold-rolled), as well as austenitic steel, various other metals (V, Nb, Ta, Mo) and some amorphous metals. The disc-pressure-test is shown to be easy and useful for determining hydrogen embrittlement. Even austenitic steel exhibits some embrittlement (x = 1.5). The strongest embrittlement occurred in amorphous metal Vitrovac 0040 with x = 9.8.     

XRD analyses on dissolution behavior of cementite in eutectoid pearlitic steel during cold rolling

The changes of lattice parameter and carbon content of cold-rolled pearlitic ferrite (α) in eutectoid pearlitic steels were studied with X-ray diffraction (XRD) analysis. The effects of rolling reduction and alloying elements on the dissolution of cementite (θ) were discussed. In the present work, it was observed that XRD peaks of pearlitic α shift to smaller angle side after cold rolling with respect to that of the as-transformed state. The lager the cold-rolling reduction is, the more significant the shift of α peaks, and the larger its lattice parameter. The addition of Cr or Mn can accelerate the dissolution of the pearlitic θ during cold rolling with the effect of Cr more pronounced, but the influence of Si is not so evident.     

Adhesion of lacquer to phosphated steel — A shear test evaluation

Measurement of the adhesion toughness of a fast cure thermosetting powder coating used for corrosion protection of cold-rolled steel has been attempted in a shear test under uniform plane stress loading conditions at the interface. A specially designed test specimen preparation procedure (by direct crosslinking) and geometry (symmetrical) was developed to enable proper mechanical behaviour under shear initiation of fracture and uniform plane stress loading in the significant section of the specimen — the interface. The shear test was designed to measure the nominal and the net ultimate shear stress values (USS)_n and (USS)_net' as well as the critical stress intensity factor (SIF) of interfaces. From experimentally measured critical load at which the adhesion failed, the ultimate shear stress values (USS_net N mm^–2) were calculated and used as a quantitative information of the bond toughness along the interfaces. The experimental results with a range of specimens revealed that the test can, indeed, discern subtle variations influencing adhesion such as type of cold-rolled steel, an iron phosphate pretreatment before coating or variation in stoving temperatures. Fractographic analysis of shear failed specimens on mating surfaces revealed generation of a microcrack network in most of the fracture pattern tested, indicating fracture mechanism transitions characteristic of pure shear for both iron phosphated free cold-rolled steel-lacquer (SL) as well as for iron phosphated cold-rolled steel-lacquer (SPL) specimens. The fractographs, however, indicate fracture propagation more difficult for SPL specimens and comparatively smooth fracture surface for SL specimens, obviously affected by variations in their respective interface structure and morphology. This behaviour correlates well with measurements of (USS)_net in test.     

Ultrafine ferrite formation through cold-rolling and annealing of low-carbon dual-phase steel

Formation process of ultrafine grained ferrite through a simple thermomechanical route composed of cold-rolling and annealing of dual-phase starting microstructures was investigated. A 0·1%C steel having a ferrite–martensite dual-phase microstructure was cold-rolled by 91% and subsequently annealed below the eutectoid (A1) temperature. During the annealing, the cold-rolled microstructure gradually changed to be equiaxed ultrafine ferrite, without preferential growth of particular ferrite grains. Hardness of the cold-rolled specimen continuously decreased without a significant drop. The main components of texture in the cold-rolled specimen, α-fibre and γ-fibre, did not change greatly after the formation of ultrafine grains. It was suggested that finely subdivided region having large misorientations in the cold-rolled state grew with recovery to form the ultrafine ferrite.     

Repetition bend properties of Cu-Cr and Cu-Cr-Sn alloys

Repetition numbers of bending of Cu-0.81 wt% Cr, Cu-0.81 wt% Cr-0.14 wt% Sn and Cu-0.26 wt% Cr-0.10 wt% Sn alloys were investigated. After solution treatment, the first two types of copper alloys have a primary chromium phase; this is not so in the last alloy. The primary chromium phase does not influence the repetition numbers of bending of cold-rolled specimens; the repetition numbers of bending of specimens aged at 723 K for 1.8 × 10³ sec after cold rolling are higher than those of cold-rolled specimens. The cause of this is considered to be a recovery of work-hardening during ageing.     

Effect of Initial Surface Quality on Final Roughness and Texture of Annealed Ni-5at.%W Tapes Coated with a Gd2Zr2O7 Buffer Layer

Surface roughness of Ni-5at.%W tapes in cold-rolled and annealed conditions after subsequent deposition of a Gd₂Zr₂O₇ buffer layer has been studied as a function of the polishing grade, taking grain boundary grooving into account. It is found that annealing decreases the initial mean surface roughness achieved by mechanical polishing of the cold-rolled material, except after very fine polishing. Furthermore, compared to the surface of the tape annealed after fine polishing, the mean roughness slightly increases after the deposition of the buffer layer. Grain boundary grooving was found to impose a lower limit for the mean surface roughness. In the annealed tapes, the fraction of orientations within 5^○ from the ideal cube orientation was observed to be very sensitive to the surface roughness before annealing.     

Thickness dependence of Gc for shear lip propagation from a single crack propagation specimen: aluminium 6061-T6 alloy,cold-rolled copper and BPA polycarbonate

Values ofG _c for ductile crack propagation in a series of double cantilever beam specimens, each with a single side groove of constant depth, increase linearly with net section thickness. If a single side groove with linearly varying depth is cut in a double cantilever beam specimen, the tapered net section thickness results in a plastic zone, the crosssection area of which increases linearly with crack length. The attendantG _c increases in proportion to the plastic zone size in such a specimen. A single properly designed tapered section specimen appears to be capable of providing estimates of (a) the dependence of shear lipG _c on shear lip width, (b) the natural shear lip width and shape, and (c) the shear lip plastic strain. G _c and plastic zone data from specimens of both kinds are reported for aluminium 6061-T6 alloy, cold-rolled copper and BPA polycarbonate. Results of uniaxial tensile tests and of centre-notch tensile tests are also reported for comparison purposes.G _cs, plastic zone sizes and plastic zone strains vary from material to material and appear to reflect in part the drawing and necking characteristics seen in uniaxial tensile tests.     

A differential scanning calorimetry study of recrystallization and its interaction with precipitation in Al-Fe-Si commercial alloys (AA1145 and AA8011)

Differential scanning calorimetry (DSC) was used to study several aspects of recrystallization in cold-rolled Al-Fe-Si commercial alloys. Two commercial alloys (AA1145 and AA8011) with different contents of Fe + Si and continuously cast in a twin roll machine, were used. It is shown that DSC allows a direct study of the interaction between the precipitation of alloying elements and recrystallization. The kinetics of recrystallization in the two alloys was also analysed, showing that the experimental data can be satisfactorily fitted with the Johnson-Mehl-Avrami equation with an exponentn = 2.5. The same kinetic parameters can be also used to fit the isothermal data obtained in the same DSC apparatus. The change in stored energy as a function of true strain is also considered.     

Orientation dependent slip in polycrystalline titanium

The factors determining the active slip systems in cold-rolled polycrystalline titanium sheet were investigated. The texture of such a sheet has an important role in determining the active slip systems. Equi-Schmid factor lines for different slip modes were calculated, and transmission electron microscopy proved that pile ups of dislocations of the predicted systems are formed. The active primary slip system was found to be the prismatic a type slip {1¯100} 11¯20 while the secondary system is either prismatic or pyramidal type I {10¯11}. Basal slip of a dislocations could in certain orientations of load direction be the primary slip systems. Dislocations of the (c + a) type play no significant role in the plastic deformation of polycrystalline titanium sheet.     

NaCl-induced accelerated oxidation of 304 stainless steel and Fe-Mn-Al alloy at 900°C

The high-temperature corrosion behavior of cold-rolled and annealed 304 stainless steel (304SS) and Fe-29Mn-8Al-2.5Si-2Cr-0.74C alloy coated with 0.002 g cm^–2 NaCl initially were studied at 900°C in air. The corrosion kinetics of the two alloys follow the parabolic rate law. The initial NaCl coating accelerates oxidation of these alloys by oxychlorination and chlorination/oxidation cyclic reactions, and catalytic actions of chloride or chlorine are thought to be the principal causes. A bulky, layered scale as well as some intergranular attack is noted on the annealed 304SS, and intergranular attack distributes over the alloy substrate of the cold-rolled 304SS during a 144 h exposure. With the formation of a compact Al₂O₃ scale to decrease further chlorine attack, the corrosion resistance of Fe-Mn-Al alloy is superior to that of 304SS in this study.     

Effects of pulsed magnetic annealing on Goss texture development in the primary recrystallization of grain-oriented electrical steel

As the condition of Goss component in primary structure of grain-oriented electrical steel plays a significant role for its abnormal growth in the subsequent secondary recrystallization, pulsed magnetic annealing was used to affect the development of Goss texture in primary recrystallized structure in this study. Specimens of one-stage cold-rolled electrical steel were annealed under pulsed magnetic field with the maximum strength 1T from three different directions—rolling direction, transverse direction, and normal direction at the temperature about 700 °C for 16 min, and then electron backscattering scanning diffraction technology was used to measure grains for texture determination. It was found that pulsed magnetic field not only decreases the average grain size of recrystallized structure but also affects the development of primary recrystallized texture varied with the change of applying direction due to that the magnetic field induces extraneous driving forces causing preferential grain growth and the preferential order can be listed from those with crystal orientation 〈100〉//H, 〈112〉//H, 〈110〉//H to 〈111〉//H. This research can be a guide to control the Goss texture development in primary recrystallization with pulsed magnetic annealing for deformed grain-oriented electrical steel.     

Broadened X-ray-diffraction profile analysis of cold-rolled aluminium-magnesium alloys

A cold-rolled, commercial pure aluminium and three aluminium-magnesium alloys (containing, respectively, 1 wt%, 3 wt% and 5 wt% magnesium) were studied by X-ray-diffraction (XRD) profile analysis. The investigated equivalent plastic deformations of the materials were ranged between 0.1 and 5.0. With increases in the amounts of magnesium, the diffraction peaks widened. For each alloy, the peak width (which gives first information from the analysis) increased for low deformation ratios and reached a maximum value, ds _max and then it decreased or stabilized. The ds _max value increased with increases in the amount of magnesium in the alloys and ranges for equivalent deformation and 1.5. The results of the X-ray profile analysis have been correlated with previous observations by transmission electron microscopy (TEM), and they have been successfully used to quantify the microstructural features of the alloys.