The effects of trace Sc and Zr on microstructure and internal friction of Zn–Al eutectoid alloy

The damping properties of Zn–22 wt.% Al alloys without and with Sc (0.55 wt.%) and Zr (0.26 wt.%) were investigated. The internal friction of the determined by the microstructure has been measured in terms of logarithmic decrement (δ) using a low frequency inverted torsion pendulum over the temperature region of 10–230 °C. An internal friction peak was separately observed at about 218 °C in the Zn–Al alloy and at about 195 °C in Zn–Al–Sc–Zr alloy. The shift of the δ peak was found to be directly attributed to the precipitation of Al₃(Sc, Zr) phases from the alloy matrix. We consider that the both internal friction peak in the alloy originates from grain boundary (GB) relaxation, but the grain boundary relaxation can also be affected by Al–Sc–Zr intermetallics at the grain boundaries, which will impede grain boundary sliding. In addition, Al–Sc–Zr intermetallics at the grain boundaries can pin grain boundaries, and inhibit the growth of grains in aging, which increases the damping stability of Zn–22 wt.% Al alloy.     

Mechanical spectroscopy in commercial Fe–6 wt.% Si alloys between 400 and 1000 K

Mechanical spectroscopy, neutron diffraction and differential scanning calorimetry (DSC) were performed on commercial Fe–6 wt.% Si alloy after quenching from high temperature. The damping spectrum shows a peak at around 800 K and an associated modulus defect. The modulus shows an increase during the second and subsequent heating runs. In addition, an anomaly in the modulus behavior has been found at around 400 K. Different thermal treatments allows to obtain two different recovery degrees of the quenched-in defects. The influence of the recovery degree on the 800 K internal friction peak and on the anelastic modulus has been evaluated and confirm the validity of the grain boundary mechanism associated to this peak. Experimental results are discussed on the basis of recovery and ordering processes.     

Electronic irradiation modification in parent Fe–Ni–C austenite and Snoek-like effects in induced alpha-martensite

Considerable changes in atomic distribution, Ni atomic ordering and elimination of inhomogeneity in distribution of carbon atoms in the -martensite occurred after high-dose electronic irradiation and subsequent deep cooling of parent Fe–22.4 at.%Ni–5.13 at.%C austenite in liquid nitrogen. These atomistic changes resulted from the electronic irradiation caused a huge increase of the 160 °C peak of internal friction in the -martensite. Discussion regarding this phenomenon brings to a conclusion on the behavior of the 160 °C peak, fitting in the best way for a certain Snoek-like relaxation in Fe–Ni–C martensite.     

Anelastic relaxation processes due oxygen in Nb–3.1 at.% Ti alloys

In the last 50 years several studies have been made to understand the relaxation mechanisms of the heavy interstitial atoms present in transition metals and their alloys. Internal friction measurements have been carried out in a Nb–Ti alloy containing 3.1 at.% of Ti produced by the Materials Department of Chemical Engineering Faculty of Lorena (Brazil), with several quantities of oxygen in solid solution using a torsion pendulum. These measurements have been performed by a torsion pendulum in the temperature range from 300 to 700 K with an oscillation frequency between 0.5 and 10 Hz. The experimental results show complex internal friction spectra that have been resolved, into a series of Debye peaks corresponding to different interactions. For each relaxation process it was possible to obtain the height and temperature of the peak, the activation energy and the relaxation time of the process.     

Internal friction associated with phase transformation of nanograined bulk Fe–25 at.% Ni alloy

The internal friction and modulus of a nanograined bulk Fe–25 at.% Ni prepared by an inert gas condensation and in situ warm consolidation technique were measured in temperature range −100 to 400 °C by means of a dynamic mechanical analyzer (DMA). An internal friction peak at around −75 °C associated with martensitic transformation was observed. During heating, an internal friction peak at about 200 °C accompanied with the decrease of modulus was also observed, which was proved by XRD that this may mainly be attributed to the reverse phase transformation of stress-induced martensite (SIM). Some abnormal features of modulus versus temperature were observed and discussed.     

Effect of nitrogen content on the degradation mechanisms of thin Ta–Si–N diffusion barriers for Cu metallization

The effect of the nitrogen content on the thermal stability and degradation mechanisms of Ta–Si–N diffusion barriers was studied using methods that prove Cu interdiffusion. On the one hand, glancing angle X-ray diffraction was applied to detect Cu₃Si formation after annealing of Cu/Ta–Si–N/Si layer stacks. On the other hand, a combined secondary ion mass spectroscopy and transmission electron microscopy analysis of Ta–Si–N/Cu/Ta–Si–N/SiO₂/Si samples was performed. For a detailed investigation of the microstructure evolution, the crystallization behavior of both Cu-capped and uncapped Ta–Si–N/Si samples was analyzed using X-ray diffraction. In the case of an uncapped Ta₇₃Si₂₇ film, Si interdiffusion from the substrate precedes the layer crystallization. The substrate influence on the crystallization process decreases with increasing N content x_N of the Ta–Si–N layer. Using Cu/Ta–Si–N/Si samples, a critical temperature for Cu silicide formation was determined. This temperature increases with increasing N content of the Ta–Si–N barrier. In the case of Ta–Si–N films with x_N > 25 at.%, Cu interdiffusion into the substrate occurs before a significant barrier crystallization is observed. For Ta–Si–N layers with x_N ≤ 25 at.%, no indications for Cu diffusion before crystalline phase formation were detected.     

Internal friction of γ-TiAl-based alloys with different microstructures

A Ti–46.5 at.% Al–4 at.% (Cr, Nb, Ta, B) intermetallic alloy with different microstructures (fine-grained primary annealed (PA) and coarse-grained fully lamellar (FL)) was examined by internal friction experiments. The influence of microstructure on the internal friction properties was studied by high-temperature (300–1270 K) mechanical loss experiments using a low frequency subresonance apparatus (0.01–10 Hz). The mechanical loss spectra show two phenomena: (i) a loss peak of Debye type at about 1000 K (1 Hz) which occurs only in samples with fully lamellar microstructure. The activation enthalpy, determined from the frequency shift, is 3.0 eV. The peak is assigned to thermally activated reversible local movement of dislocations that are part of the mismatch structure of semicoherent lamellar interfaces. (ii) A high-temperature damping background above 1000 K which is controlled by an activation enthalpy of 3.8–3.9 eV. The activation enthalpy agrees well with that of creep and strain rate cycling tests (3.5–3.7 eV) and is in the range of values reported for self-diffusion indicating that both properties (high-temperature background (HTB) and creep) are controlled by volume diffusion assisted climb of dislocations.     

Low-temperature liquid-phase epitaxy growth from Ga–As–Bi solution

Measurements of Ga–As–Bi liquidus composition at 600 °C for Ga–Bi–GaAs range are reported. High quality GaAs layers and Al_0.28Ga_0.72As/GaAs single quantum well (SQW) structures with different well thicknesses are grown from a mixed Ga + Bi solvent by low-temperature liquid-phase epitaxy method. They are characterized by the Hall effect and photoluminescence (PL) measurements. Significant changes in the layer electrical properties are observed with varying the Bi content in the solution. The layers grown from a mixed solution with 20–30% Bi content are n-type with carrier concentration of 10¹⁴ cm^− 3 and mobility of 40 000 cm²/Vs at 77 K, while p-type high resistivity layers are obtained from a solution with more than 70% Bi content. PL spectra of the SQW structures grown from Ga + 25% Bi solution at 2 K show that the roughness at the interface is less than two monolayers.     

Fracture behavior and mechanical properties of Mg–4Y–2Nd–1Gd–0.4Zr (wt.%) alloy at room temperature

The microstructure, mechanical properties and fracture behavior of gravity die cast Mg–4Y–2Nd–1Gd–0.4Zr (wt.%) (WNG421) alloy are studied at room temperature in different thermal conditions, including as-cast, solution-treated and different aging-treated (both isothermal and two-step aging) conditions. The results indicate that WNG421 alloy shows different behaviors of crack initiation and propagation in different thermal conditions during tensile test at room temperature. After pre-aged at 200 °C for 5 h, the hardness of WNG421 alloy first reduces and then increases when secondary aged at 250 °C (two-step aging). The peak hardness and corresponding tensile strength of the two-step aged alloy both increases compared with those in 250 °C isothermal peak-aged condition. Tensile strength of WNG421 alloy at room temperature in low temperature (200 °C) isothermal peak-aged condition is much higher than that in high temperature (250 °C) isothermal peak-aged condition.     

Internal friction during martensitic transformation in high manganese Mn–Cu alloys

Low-frequency internal friction and elastic modulus were studied for manganese-rich Mn–Cu alloys in the temperature range of martensitic transformation (20–300 °C). It is shown that the some special features of the transformation peak and its temperature are caused by the degree of the spinodal decomposition. The phenomenological model connecting an-elastic effects with the stages of evolution of the structure during martensitic transformation in manganese-rich Mn–Cu alloys (tweed structure–“parquet” structure–classical twinning martensite) is presented.     

Characteristics of Ti–Ni–Pd shape memory alloy thin films

Ti–Ni–Pd thin films were deposited by RF magnetron sputtering. Microstructure and phase transformation behaviors were studied by X-ray diffraction (XRD), by transmission electron microscopy and by differential scanning calorimeter (DSC). Also tensile tests and the internal friction characteristics were examined. Annealing at 750 °C followed by subsequent annealing at 450 °C resulted in relatively homogeneous microstructure and uniform martensite/austenite transformation. The results from DSC showed clearly the martensitic transformation upon heating and cooling, the transformation temperatures are 112 °C (M* peak) and 91 °C (M peak), respectively. The transformation characteristics are also found in strain–temperature curves and internal friction–temperature curves. The film had shape memory effect. The frequency had no effect on the modulus, but the internal friction decreased with increasing frequency.     

High-temperature internal friction on TiAl intermetallics

In order to study the microscopic mechanisms controlling the plastic deformation at high temperature of two γ-TiAl alloys with nominal compositions: Ti–46.5Al–4(Cr, Nb, Ta, B) and Ti–45Al–(5–10)Nb (in at.%), internal friction (IF) measurements have been performed. A subresonant torsion pendulum has been used working in two different modes; changing the temperature between 300 and 1200 K at a constant frequency, and varying the frequency between 0.001 and 10 Hz at a fixed temperature. The resulting mechanical spectra show an anelastic relaxation peak at about 1060 K at 1 Hz in one of the alloys and a high-temperature background in both of them. Activation parameters of the loss peak have been calculated and an activation enthalpy of about 3.8 eV is obtained. The characteristics and a possible responsible mechanism for this relaxation peak are discussed.     

Effects of heat treatments on the microstructures and mechanical properties of Mg–3Nd–0.2Zn–0.4Zr (wt.%) alloy

Microstructure and mechanical properties of as-cast and different heat treated Mg–3Nd–0.2Zn–0.4Zr (wt.%) (NZ30K) alloys were investigated. The as-cast alloy was comprised of magnesium matrix and Mg₁₂Nd eutectic compounds. After solution treatment at 540 °C for 6 h, the eutectic compounds dissolved into the matrix and small Zr-containing particles precipitated at grain interiors. Further aging at low temperatures led to plate-shaped metastable precipitates, which strengthened the alloy. Peak-aged at 200 °C for 10–16 h, fine β″ particles with DO₁₉ structure was the dominant strengthening phase. The alloy had ultimate tensile strength (UTS) and elongation of 300–305 MPa and 11%, respectively. Aged at 250 °C for 10 h, coarse β′ particles with fcc structure was the dominant strengthening phase. The alloy showed UTS and elongation of 265 MPa and 20%, respectively. Yield strengths (YS) of these two aged conditions were in the same level, about 140 MPa. Precipitation strengthening was the largest contributor (about 60%) to the strength in these two aged conditions. The hardness of aged NZ30K alloy seemed to correspond to UTS not YS.     

Aging behaviour of Al–Cu–Mg alloy–SiC composites

The age-hardening kinetics of powder metallurgy processed Al–Cu–Mg alloy and composites with 5, 15 or 25 vol.% SiC reinforcements, subjected to solution treatment at 495 °C for 0.5 h or at 504 °C for 4 h followed by aging at 191 °C, have been studied. The Al–SiC interfaces in composites show undissolved, coarse intermetallic precipitates rich in Cu, Fe, and Mg, with its extent varying with processing conditions. Examination of aging kinetics indicates that the peak-age hardness values are higher, and the time taken for peak aging is an hour longer on solutionizing at 504 °C for 4 h, due to greater solute dissolution. Contrary to the accepted view, the composites have taken longer time to peak-age than the alloy, probably due to lower vacancy concentration, large-scale interfacial segregation of alloying elements, and inadequate density of dislocations in matrix. The composite with 5 vol.% SiC with the lowest inter-particle spacing has shown the highest hardness.     

Corrosion of magnesia–chrome brick in molten MgO–Al2O3–SiO2–CaO–FetO slag

The corrosion of magnesia–chrome (MgO–Cr₂O₃) brick in molten MgO–Al₂O₃–SiO₂–CaO–Fe_tO slag has been characterized using a dynamic rotary slag corrosion testing for various test cycles at 1650 °C. The open porosity decreases from 15.3 to 4.0% for three cycles, then it gradually increases from 4.0 to 4.8% when the test is extended to nine cycles, in which the permeating depth of the slag maintains at about 20 mm. The XRD pattern of the permeated layer shows the presence of the MgO, MgCr₂O₄ and CaMgSiO₄ phases. In the interior of the permeating layer cracks are formed and corrosion starts at the pores and cracks of MgO and decreases gradually. However, at 20–40 mm beneath the permeated layer edge, different shapes of MgO particles are found.     

Fatigue strength of Ti–6Al–4V at very long lives

The objective of this research was to investigate the fatigue strength of Ti–6Al–4V using an ultrasonic fatigue system. Fatigue testing up to 10⁹ cycles under fully reversed loading was performed to determine the ultra-high cycle fatigue behavior of Ti–6Al–4V. Endurance limit results were compared to similar data generated on conventional servohydraulic test systems and electromagnetic shaker systems to determine if there are any frequency effects. Fatigue specimens were tested with and without cooling air to determine the effects of increased specimen temperature caused by internal damping due to cycling at a very high frequency. An infrared camera was also used to record specimen temperatures at various load levels. Results indicate that the effects of frequency, including internal heating, on the very high cycle fatigue behavior of Ti–6Al–4V are negligible under fully reversed loading conditions.     

Internal friction of hydrogen-doped metallic glasses of high glass forming ability

Seven multi-component metallic glasses of high glass forming ability (four Zr-based, a Mg-based, a Pd-based and a La-based glasses) have been hydrogenized electrolytically and internal friction has been measured at temperatures between 80 and 400 K. Hydrogen damping has been observed in every alloy; the internal friction peak is quite broad, where the peak value increases and then decreases and the peak temperature decreases with increasing hydrogen content. Compared with the results of the hydrogen damping in binary metallic glasses so far reported, the peak height versus peak temperature relation is generally shifted to higher temperature side in multi-component glasses, the origin of which has been discussed.     

Fatigue behaviour of monotectoid-based Zn–Al–Cu alloys in 3.5% NaCl and 1% HCl solutions

One binary Zn–40Al and three Zn–40Al-based ternary alloys containing 1%, 3%, and 5% Cu were produced by permanent mold casting. Their fatigue behavior was investigated in 3.5% NaCl and 1% HCl solutions by a rotary bending fatigue test machine at a frequency of 33.3 Hz. The stress amplitude versus number of cycles to failure (S–N) curves of the alloys was plotted for both environments. Corrosion degradation factors of the alloys were determined. The corrosion environments reduced the fatigue strength and fatigue life of the alloys considerably. However, acid solution was found to be more detrimental for these alloys than the salt water. In addition, copper content was found to be less effective on the fatigue strength and fatigue life of the alloys in both salt water and acid solution than it was in air. Corrosion degradation factor of the alloys increased with increasing copper content up to approximately 3%, above which it decreased as the copper content increased. It was also shown that the fatigue data obtained from the monotectoid-based Zn–Al–Cu alloys in the corrosive environments obey the Basquin's law.     

The effects of mischmetal, cooling rate and heat treatment on the hardness of A319.1, A356.2 and A413.1 Al–Si casting alloys

The present study investigated the effect of mischmetal as a modifier, as well as the effects of cooling rate and heat treatment on the hardness of non-modified and Sr-modified A319.1, A356.2 and A413.1 Al–Si casting alloys. The main aim of the study was to determine the effect of mischmetal in terms of mischmetal-containing intermetallic phases, as well as the effects of the chemical composition of the alloys, cooling rate and heat treatment on the corresponding hardness values obtained for the alloys in question. Two cooling rates were employed to provide estimated hardness levels of 85 and 110–115 BHN, levels conforming to levels most commonly observed in commercial applications of these alloys.

The hardness measurements revealed that the hardness values of the as-cast alloys were higher at high cooling rates than at low cooling rates. Non-modified alloys (i.e. those with no Sr addition) displayed slightly higher hardness levels compared to the Sr-modified alloys. Also, the hardness decreased with the addition of mischmetal at both cooling rates.

Two peak hardness values were observed at 200 °C/5 h and 240 °C/5 h at high cooling rates in the non-modified A319.1 alloy after aging at different temperatures between 155 °C/5 h and 240 °C/5 h, while the Sr-modified alloy showed only one peak at 200 °C/5 h. Two maximum hardness values were observed at 155 °C/5 h and 180 °C/5 h in both non-modified and Sr-modified alloys at low cooling rates. The alloys containing 0 and 2 wt% mischmetal additions exhibited the highest hardness values at both cooling rates; the hardness decreased with further mischmetal additions.

Peak hardness was observed at 180 °C/5 h in the non-modified and Sr-modified A356.2 alloys under both cooling rate conditions after aging at different temperatures between 155 °C/5 h and 240 °C/5 h. The alloys free of mischmetal exhibited relatively higher levels of hardness than those containing mischmetal. The hardness decreased with increasing mischmetal addition. At the high cooling rates, the non-modified alloys displayed higher hardness values than the Sr-modified alloys, while an opposite trend was observed at the low cooling rate.

The decrease in the hardness values may be attributed to the interaction of the mischmetal with the alloying elements Cu and Mg to form the various intermetallic phases observed. In tying up these elements, the volume fraction of the precipitation-hardening phases formed in the A319.1 and A356.2 alloys (i.e. the Al₂Cu and Mg₂Si phases) is significantly reduced, thereby decreasing the hardness. The addition of mischmetal was also reported to change the precipitation sequence of the Mg₂Si phase in the A356.2 alloy. In the case of the A413.1 alloy, the low content of alloying elements resulted in a weak response of the alloy to the age-hardening process at all aging temperature/time conditions (155 °C/5 h–240 °C/5 h), and at both cooling rates. Thus, no peak hardness was observable in these alloys.     

Synthesis of in situ Al–TiB2 composites using stir cast route

When elemental Ti and B powders were added to molten Al at above 1000°C, fine in situ TiB₂ particulates were formed through Al–Ti–B exothermic reaction. By optimising the nucleation of TiB₂, the tensile and yield strengths of a synthesised Al–15V_f%TiB_s composite were twice that of matrix material. Modification of Al-matrix with 4.5 wt%Cu tripled the tensile and yield strengths at peak-aged condition. Owing to the co-presence of brittle Al₃Ti flakes with TiB₂ particles in the composites synthesised by the Al–Ti–B system, ductility was reduced to 68% and 84% in composites with Al- and Al–Cu matrices, respectively. When the (Ti + B) mixture was incorporated with 3 wt%C, TiB₂ and TiC reinforcing phases were simultaneously produced in the composite with Al–Cu matrix. Such an approach reduced Al₃Ti compound in the composite considerably. Although the presence of Cu in the composite was found to promote the formation of Al₃Ti, its effect on the fluidity caused the melt recovery to increase from 33% to 52%.