Effect of Initial Annealing Temperature on Microstructural Development and Microhardness in High‐Purity Copper Processed by High‐Pressure Torsion

The effect of the initial annealing temperature on the evolution of microstructure and microhardness in high purity OFHC Cu is investigated after processing by HPT. Disks of Cu are annealed for 1 h at two different annealing temperatures, 400 and 800 °C, and then processed by HPT at room temperature under a pressure of 6.0 GPa for 1/4, 1/2, 1, 5, and 10 turns. Samples are stored for 6 months after HPT processing to examine the self‐annealing effects. Electron backscattered diffraction (EBSD) measurements are recorded for each disk at three positions: center, mid‐radius, and near edge. Microhardness measurements are also recorded along the diameters of each disk. Both alloys show rapid hardening and then strain softening in the very early stages of straining due to self‐annealing with a clear delay in the onset of softening in the alloy initially annealed at 800 °C. This delay is due to the relatively larger initial grain size compared to the alloy initially annealed at 400 °C. The final microstructures consist of homogeneous fine grains having average sizes of ≈0.28 and ≈0.34 µm for the alloys initially annealed at 400 and 800 °C, respectively. A new model is proposed to describe the behavior of the hardness evolution by HPT in high purity OFHC Cu.     

Effect of Zr on microstructure and mechanical properties of the Al–Cu–Er alloy

ABSTRACT

The microstructure and mechanical properties of the Al–4Cu–2.7Er–0.3Zr alloy were investigated. The precipitates of the L1₂ structured phase with sizes 37?±?12?nm were formed in lines and homogenously distributed inside the aluminium matrix after annealing at 605°C for 1?h. The as-rolled Al–4Cu–2.7Er–0.3Zr alloy developed an increased hardness after 1?h annealing at 100–550°C and 0.5–6?h annealing at 150–250°C due to precipitation of the Al₃(Er,Zr) phase. Addition of Zirconium improved the tensile properties relative to those of the Zr-free alloy by approximately 20?MPa: yield strength?=?273–296?MPa and ultimate tensile strength?=?296–328?MPa in the alloys annealed at 100–150°C.     

Optimizing strength and ductility in Cu–Al alloy with recrystallized nanostructures formed by simple cold rolling and annealing

A single-phase Cu–Al alloy with a low stacking fault energy was processed by cold rolling and subsequent annealing. Fully recrystallized microstructures composed of ultrafine grains were obtained after isothermal annealing at different temperatures. The minimum mean grain sizes achieved were below 1 μm. It was found that the microstructures were homogeneous after annealing at 400 °C, but somehow inhomogeneous after annealing at lower temperature of 300 °C and higher temperature of 550 °C. Superior strength and ductility were obtained by controlling the grain size of the microstructures. After annealing at 400 °C for 10 s, a fully and homogeneously recrystallized material with mean grain size of 770 nm was produced, which had a high yield strength of 524.2 MPa and a remarkable uniform elongation of 15.7 %.     

Annealing characteristics of nanostructured Cu-Fe-P alloy processed by accumulative roll-bonding

Annealing characteristics of a nanostructured copper alloy processed by accumulative roll-bonding (ARB) were studied. A nano-grained Cu-Fe-P alloy processed by 8 cycles of the ARB was annealed at various temperatures ranging from 100 to 400 degrees C for 0.6 ks. The sample still showed an ultrafine grained (UFG) structure up to 250 degrees C, however above 300 degrees C it began to replace by equiaxed and coarse grains due to an occurrence of the conventional static recrystallization. The hardness of the annealed copper decreased largely above 300 degrees C. These annealing characteristics of the UFG copper alloy were compared to those of a high purity copper.     

Effects of post-annealing on the microstructure and mechanical properties of friction stir processed Al–Mg–TiO2 nanocomposites

Aluminum matrix nanocomposites were fabricated via friction stir processing of an Al–Mg alloy with pre-inserted TiO₂ nanoparticles at different volume fractions of 3%, 5% and 6%. The nanocomposites were annealed at 300–500 °C for 1–5 h in air to study the effect of annealing on the microstructural changes and mechanical properties. Microstructural studies by scanning and transmission electron microscopy showed that new phases were formed during friction stir processing due to chemical reactions at the interface of TiO₂ with the aluminum matrix alloy. Reactive annealing completed the solid-state reactions, which led to a significant improvement in the ductility of the nanocomposites (more than three times) without deteriorating their tensile strength and hardness. Evaluation of the grain structure revealed that the presence of TiO₂ nanoparticles refined the grains during friction stir processing while the in situ formed nanoparticles hindered the grain growth upon the post-annealing treatment. Abnormal grain growth was observed after a prolonged annealing at 500 °C. The highest strength and ductility were obtained for the nanocomposites annealed at 400 °C for 3 h.     

Tensile properties and fracture behaviour of an ultrafine grained Ti–47Al–2Cr (at.%) alloy at room and elevated temperatures

An ultrafine grained (UFG) Ti–47Al–2Cr (at.%) alloy has been synthesized using a combination of high energy mechanical milling and hot isostatic pressing (HIP) of a Ti/Al/Cr composite powder compact. The material produced has been tensile tested at room temperature, 700 and 800 °C, respectively, and the microstructure of the as-HIPed material and the microstructure and fracture surfaces of the tensile tested specimens have been examined using X-ray diffractometry, optical microscopy, scanning electron microscopy and transmission electron microscopy. The alloy shows no ductility during tensile testing at room temperature and 700 °C, respectively, but very high ductility (elongation to fracture 70–100%) when tensile tested 800 °C, indicating that its brittle to ductile transition temperature (BDTT) falls within the temperature range of 700–800 °C. The retaining of ultrafine fine equiaxed grain morphology after the large amount of plastic deformation of the specimens tensile tested at 800 °C and the clear morphology of individual grains in the fractured surface indicate that grain boundary sliding is the predominant deformation mechanism of plastic deformation of the UFG TiAl based alloy at 800 °C. Cavitation occurs at locations fairly uniformly distributed throughout the gauge length sections of the specimens tensile tested at 800 °C, again supporting the postulation that grain boundary sliding is the dominant mechanism of the plastic deformation of the UFG TiAl alloys at temperatures above their BDTT. The high ductility of the UFG alloy at 800 °C and its fairly low BDTT indicates that the material a highly favourable precursor for secondary thermomechanical processing.     

Mechanical properties of ultrafine grained ferritic steel sheets fabricated by rolling and annealing of duplex microstructure

A new route to fabricate ultrafine grained (UFG) ferritic steel sheets without severe plastic deformation is proposed in this article. A low-carbon steel sheet with a duplex microstructure composed of ferrite and martensite was cold-rolled to a reduction of 91% in thickness, and then annealed at 620–700 °C. The microstructure obtained through the process with annealing temperatures below 700 °C was the UFG ferrite including fine cementite particles homogenously dispersed. The grain size of ferrite matrix changed from 0.49 to 1.0 μm depending on the annealing temperature. Dynamic tensile properties of the produced UFG steels were investigated. The obtained UFG ferrite–cementite steels without martensite phase showed high strain rate sensitivity in flow stress. The UFG ferritic steels are expected to have high potential to absorb crash energy when applied to automobile body.     

Effect of annealing on precipitation, microstructural stability, and mechanical properties of cryorolled Al 6063 alloy

The effect of annealing on precipitation, microstructural stability, and mechanical properties of cryorolled Al 6063 alloy has been investigated in the present work employing hardness measurements, tensile test, XRD, DSC, EBSD, and TEM. The solution-treated bulk Al 6063 alloy was subjected to cryorolling to produce ultrafine grain structures and subsequently annealing treatment to investigate its thermal stability. The CR Al 6063 alloys with ultrafine-grained microstructure are thermally stable up to 250 °C as observed in the present work. Within the range of 150–225 °C, the size of small precipitate particles is <1 μm. These small precipitate particles pin the grain boundaries due to Zener drag effect, due to which the grain growth is retarded. The hardness and tensile strength of the cryorolled Al 6063 alloys have decreased upon subjecting it to annealing treatment (150–250 °C).     

Effect of annealing treatment on the microstructure and mechanical properties of ultrafine-grained aluminum

Microstructural and property evolution of commercial pure Al subjected to multi-axil compression (MAC) and subsequent annealing treatment were investigated. After series of MAC pressings up to 15 passes, the samples were annealed at different temperatures. The deformed and deformed with sequent annealing treatment samples were characterized by X-ray diffraction, electron back scatter diffraction (EBSD), transmission electron microscopy (TEM) and tensile tests. The present results showed that on annealing the grain structures coarsen and transform from lamellar to equiaxed ones. Remarkably, the fraction of high angle grain boundaries drastically increases from 29.3% to 76.3% after annealing at 60 °C. Meanwhile, a significant decrease of lattice microstrain is observed after annealing, from 0.0839% to 0.0731% at 130 °C. A controlled 30 min annealing treatment on ultrafine-grained (UFG) Al at 60 °C can result obviously in a higher strength and a lower elongation, which may be associated with the nucleation and subsequent motion of dislocations in grain boundaries. As the annealing temperature is above 60 °C, the yield strength decreases and elongation increases gradually, which is attributed to the grain coarsening and microstructural enhancement.     

Microstructure,precipitates and mechanical properties of powder bed fused inconel 718 before and after heat treatment

IN718 alloy was fabricated by laser powder bed fusion (PBF) for examination of microstructure, precipitates and mechanical properties in the as-built state and after different heat treatments. The as-built alloy had a characteristic fine cellular-dendritic microstructure with Nb, Mo and Ti segregated along the interdendritic region and cellular boundary. The as-built alloys were then subjected to solution heat treatment (SHT) at 980 °C or 1065 °C for 1 h. SHT at 980 °C led to the formation of δ-phase in the interdendritic region or cellular boundary. The segregation was completely removed by the SHT at 1065 °C, but recrystallization was observed, and the carbides decorated along the grain boundaries. The as-built alloy and alloys with SHT at 980 °C and 1065 °C were two-step aged, which consisted of annealing at 720 °C for 8 h followed by annealing at 620 °C for 8 h. Transmission electron microscopy revealed the precipitation of γ' and γ” in all alloys after two-step aging, but the amount and uniformity of distribution varied. The Vickers hardness of the PBF IN718 alloy increased from 296 HV to 467 HV after direct aging. The hardness decreased to 267 HV and 235 HV after SHT at 980 °C and 1065 °C, respectively, but increased to 458 HV and 477 HV followed by aging. The evolution of Young’s modulus after heat treatment exhibited similar trend to that of hardness. The highest hardness was observed for IN718 after SHT at 1065 °C and two-step aging due to precipitation with greater amount and uniform distribution.     

Effect of initial grain size on the joint properties of friction stir welded aluminum

In this study, 2 mm-thick commercial 1050-Al plates with an ultrafine grained (UFG) structure were obtained by the accumulative roll bonding (ARB) technique after a 5 cycle process and were subsequently joined by friction stir welding (FSW) at various revolution pitches (welding speed/rotation speed) of 1 mm/r, 1.67 mm/r and 2.5 mm/r. To understand the effect of the initial grain size on the welding properties, ARB processed samples followed by annealing under H24 conditions as well as the as-received samples in the fully annealed state were also applied to the FSW process. The microstructure evolution and Vickers hardness in the stir zone of all the samples were investigated. It was revealed that the annealed samples with an intermediate grain size finally obtained the most refined grain size and highest value of Vickers hardness in the stir zone. However, for the UFG samples, significant grain growth and corresponding decrease in hardness can be found in the stir zone.     

Effect of quenching on microstructure and wear‐resistance of Fe–10Cr–1.5B–2Al Alloy

Cast Fe–10Cr–1.5B–2Al alloy was quenched at different temperatures. The effects of quenching temperature on microstructure and hardness and wear‐resistance of Fe–10Cr–1.5B–2.0Al alloy were investigated by means of the optical microscopy, the scanning electron microscope, X‐ray diffraction, energy dispersive spectrometer, Vickers hardness and Rockwell hardness tester, and the MM‐200 block‐on‐ring wear testing machine under dry friction condition. The results indicate that the as‐cast microstructure of Fe–10Cr–1.5B–2.0Al alloy consists of ferrite, pearlite and netlike eutectics which are distributed in the grain boundary. The eutectics mainly include herringbone M₂B and chrysanthemum M₇(C, B)₃. The matrix gradually turns into single martensite with the increase of the quenching temperature. The type of borocarbides has no obvious change after quenching. The netlike boride almost totally fractures and transforms from the fish‐bone structure to the graininess. There is some retained austenite in the quenched structures when the quenching temperature is more than 1100 °C. When the quenching temperature is in a range of 1000 °C to 1100 °C, the hardness and wear resistance show a sharp increase with an increase of temperature, and show a slight decrease after surpassing 1100 °C.     

Structure and mechanical properties of the annealed TZAV-30 alloy

The Ti–30Zr–5Al–3V (wt.%, TZAV-30) alloy having good mechanical properties is a potential structural material to apply in the aerospace industry. The microstructure and mechanical properties of ZTAV-30 alloy underwent various annealing heat treatments were investigated. The specimens annealed from 500 to 800 °C are composed of α and β two phases. No compound is detected in specimens annealed in that temperature range. The microstructure of annealed specimens is characterized as a typical basketweave microstructure. Three microstructural parameters, thickness of plate α phase, relative fraction of β phase and aspect ratio of α grains, were measured in those annealed specimens. As the alloy annealed in the range from 500 to 800 °C, the average thickness of plate α grains increases with the increasing annealing temperature from 500 to 700 °C but decreases while annealed at 800 °C. The fraction of retained β phase increases with annealing temperature. And the aspect ratio of plate α grains decreases firstly but increases while the annealing temperature is higher than 700 °C. As the variation of those three microstructural parameters, the strength of examined alloy varies from 1269 to 1355 MPa for tensile strength and from 1101 to 1190 MPa for yield strength, inversely, the elongation changes in the range from 12.7% to 8.4%. The strengthening and toughening mechanism of the TZAV-30 alloy with basketweave microstructure is also discussed in this paper.     

Service properties of ultrafine-grained Ti–6Al–4V alloy at elevated temperature

This study deals with investigation of mechanical properties and fatigue behavior of the ultra-fine grained (UFG) alloy Ti–6Al–4V at elevated temperatures. UFG samples were produced by means of combination of equal-channel angular pressing and thermomechanical treatments. Studies of the temperature dependence of mechanical properties of the UFG alloy demonstrated their thermal stability upto 175–350 °C. It was revealed that 100-hour creep rupture strength at 300 °C increased from 750 MPa in the conventional state to 890 MPa in the UFG state. The alloy demonstrates stability of the UFG structure at 300 and 370 °C in the conditions of long-term tests. The fatigue tests were conducted with axial loading applied on a sample at 175 °C, the asymmetry factor of the cycle was 0.1. The fatigue endurance limit of the UFG alloy was almost 50 % higher than that of the CG alloy.     

Hot deformation of ultrafine-grained Al6063/Al2O3 nanocomposites

Ultrafine-grained (UFG) Al6063 alloy reinforced with 0.8 vol% nanometric alumina particles (25 nm) was prepared by reactive mechanical alloying and direct powder extrusion. Transmission electron microscopy and electron backscatter diffraction analysis showed that the grain structure of the nanocomposite composed of nanosize grains (<0.1 μm), ultrafine grains (0.1–1 μm) and micronsize grains (>1 μm) with random orientations. Mechanical properties of the material were examined at room and high temperatures by compression test. It was found that the yield strength of the UFG composite material is mainly controlled by the Orowan mechanism rather than the grain boundaries. The deformation activation energy at temperature ranges of T < 300 °C and 300 °C ≤ T < 450 °C was determined to be 74 and 264 kJ mol⁻¹, respectively. This observation indicated a change in the deformation mechanism at around 300 °C. At the higher temperatures, significant deformation softening was observed due to dynamic recrystallization of non-equilibrium grain boundaries. The reinforcement nanoparticles, however, renders the high strength of the material at the elevated temperatures mainly by dislocation pinning.     

Recrystallization and fracture characteristics of thin copper wire

In this study, the annealed effect (at 150 °C ∼ 250 °C for 1 h) on the tensile mechanical properties of thin copper wires with φ = 25 μm (1 mil) was investigated. The microstructural characteristics and the mechanical properties before and after an electric flame-off (EFO) were also studied. Results indicate that with annealing temperatures of more than 200 °C, the wires possessed a fully annealed structure, the tensile strength and the hardness decreased, and the elongation was raised significantly. Through recrystallization, equiaxed grains and a few annealed twins formed in the matrix structure. The microstructures of the free air ball (FAB) of the various wires after EFO contained column-like grains. The column-like grains grew from the heat-affected zone (HAZ) to the Cu ball, and the preferred orientation was <100>. According to Weibull’s reliability analysis, the failure rates of all the specimens were the modus of wear-failure. The tensile strength and the reliability of both the 200 °C and 250 °C annealed wires in the HAZs showed the highest values of all.     

Effect of substrate temperature on properties of Cu(In,Ga, Al)Se<Subscript>2</Subscript> films grown by magnetron sputtering

Cu(In, Ga, Al)Se₂ (CIGAS) thin films were deposited by magnetron sputtering on Si(100) and soda-lime glass substrates at different substrate temperatures, followed by post-deposition annealing at 350 or 520 °C for 5 h in vacuum. Electron probe micro-analysis and secondary ion mass spectroscopy were used to determine the composition of the films and the distribution of Al across the film thickness, respectively. X-ray diffraction analysis showed that the (112) peak of CIGAS films shifts to higher 2θ values with increasing substrate temperature but remains unchanged when the films were annealed at 520 °C for 5 h. Scanning electron microscopy and atomic force microscopy images revealed dense and well-defined grains for both as-deposited and annealed films. However, notable increase in grain size and roughness was observed for films deposited at 500 °C. The bandgap of CIGAS films was determined from the optical transmittance and reflectance spectra and was found to increase as the substrate temperature was increased.     

Grain growth and mechanical properties in bulk polycrystalline silicon

The grain structure of bulk polycrystalline silicon has been examined as a function of annealing temperatures and times between 1000 and 1400°C and 6 to 24 hours, respectively. The initial high aspect grain structure decomposes into roughly equiaxed grains at 1000°C over the course of 24 hours. The grains proceed to grow via Oswald ripening with an activation energy for grain growth of 1.49 eV. The hardness increases slightly during annealing and the subsequent transformation to an equiaxed grain structure, from a Vickers hardness of 964 to 1160 kg/mm². The fracture toughness is 0.8 MPa(m)^1/2in the as grown structure, and increases to 1 MPa(m)^1/2in annealed samples. The hardness and fracture toughness are independent of grain size for grain diameters between 2.7 and 4 m.     

Effect of annealing and aging treatment on mechanical properties of ultrafine grained Al 6061 alloy

Abstract

A comparative study of aging and a combined treatment of short annealing and aging on mechanical properties and microstructure of cryorolled (CR) Al 6061 alloy is investigated in the present work by using tensile tests, hardness tests, electron backscattered diffraction and transmission electron microscope. The pre-CR solid solution treatment combined with post-CR short annealing (200°C, 5 min) followed by aging treatment (100°C, 57 h) of the Al 6061 alloy showed an improved ductility and well defined ultrafine grain structure as compared to the samples subjected to pre-CR solid solution treatment followed by post-CR aging treatment (100°C, 60 h).     

Effect of Hf additions on phase transformation,microstructural stability,and hardness of nanocrystalline 304L stainless steels synthesized by mechanical alloying

304L stainless steels with Hf additions were nanostructured by mechanical alloying (MA) and annealed at temperatures up to 1100 °C. The results showed that face-centered cubic (fcc) phase in 304L transformed to body-centered cubic (bcc) phase during MA. The in-situ studies revealed that bcc-to-fcc phase transformation completed after 105 min annealing at 900 °C for 304L, whereas Hf addition increased the required time and temperature for the complete transformation. The grain size of 304L stainless steel was ~10 nm after MA and remained ~167 and ~293 nm after annealing at 900 and 1100 °C, respectively, with Hf addition in comparison to 960 nm average grain size of base 304L stainless steel after annealing at 900 °C. The hardness of 304L increased from ~200 HV to 408 HV after MA and remained 329 HV after annealing at 1100 °C with Hf addition as opposed to 195 HV hardness of 304L.