Optimum Annealing Treatment Research Articles

Influence of Medium–High Temperature Annealing on Microstructure and Properties of High-Power Laser Melting Deposited Ti-6Al-4V Alloy

A high-power laser melting deposition (HP-LMD) device with a maximum output of 5 kW was developed to enhance the production efficiency of fabricating large-scale titanium components. In this study, the medium–high temperature annealing strategy was proposed, wherein the effects of holding temperature and holding time on the residual stress, microstructure evolution, and mechanical properties of the fabricated block were evaluated. The results showed that the residual stress on the surface of the fabricated blocks reduced significantly after annealing treatment. The microstructure of as-deposited Ti-6Al-4V alloy mainly consisted of α’ martensite and basket-weave microstructure, and the aspect ratio of the martensite decreased from 22 to 6 with the increases in annealing temperature and holding time. In addition, the annealing treatments had a favorable benefit on the microhardness and tensile performance of the HP-LMD fabricated Ti-6Al-4V alloy. The optimum annealing treatment was 650 °C/2 h followed by furnace cooling. The tensile samples processed by the optimum annealing treatment exhibited excellent properties with a yield strength of 912 MPa and an elongation of 11.48%, which far exceeded the Chinese aviation standard. In addition, the results of the statistical analysis revealed that the tensile properties of heat-treated samples were superior to as-deposited samples when the aspect ratio of martensite was in the range of 9–14. The fracture mode of both the as-deposited samples and annealed samples was ductile fracture.

Evolution of microstructure and crystallographic texture of Ni-Mn-Ga melt-spun ribbons exhibiting 1.15% magnetic field-induced strain

The microstructure and texture evolution of 10M Ni-Mn-Ga melt-spun ribbons were thoroughly evaluated by high-energy synchrotron radiation and electron backscatter diffraction. The as-spun ribbons were subjected to annealing treatment in order to tailor microstructure, atomic order degree, and crystallographic texture. The optimum annealing treatment at 1173 K for 72 h produced a homogenous <100> fiber texture and induced grain growth to the size that spans the entire ribbon thickness. This in turn reduced microstructural constraints for twin variant reorientation in the direction perpendicular to the ribbon surface. On the other hand, a homogenous radial microstructure ensured in-plane stress/strain compatibility giving rise to strain accommodation during variant reorientation. Particular attention was also given to the evaluation of atomic order, which to the largest extent controls the characteristic transformation temperatures. It also lowered the twinning stress to a level sufficiently low for martensitic variant reorientation under magnetic field. As a result, 1.15% magnetic field-induced strain without the aid of mechanical training in the self-accommodated state was achieved.

Improvement of Mechanical Strength of a Hot-Worked Twinning-Induced Plasticity Steel through an Optimum Secondary Annealing Treatment

The microstructure of the twinning-induced plasticity (TWIP) steel microalloyed by Ti (TWIP-Ti) exhibited a wide grain size distribution after applying a thermomechanical treatment. The presence of fine and coarsest grains affected mechanical twinning and properties. This research was directed toward elucidating the effect of an optimum secondary annealing treatment to produce a homogenous microstructure through the release of remnant energy stored during the hot deformation processing of a TWIP-Ti steel. A comprehensive analysis of the effect of annealing parameters on the microstructure and its enhanced mechanical properties in terms of grain size distribution, precipitation strengthening and annealing twin fraction was performed. The microstructural characterization included light optical microscopy and scanning electron microscopy (SEM). SEM line scans were performed to characterize precipitate particles found in the TWIP-Ti steel. Microhardness and tensile tests were performed on the base material (as-solution condition) and post-annealing samples. The Taguchi method was applied to optimize the annealing parameters. Furthermore, image processing was employed to quantify the grain size distribution and annealing twin fraction. The analysis results revealed that upon completion of the second stage of annealing treatment with the optimal parameters, the grain size heterogeneity decreased due to the effect of coarsest grain subdivision. The low SFE of the TWIP-Ti steel, homogenous grain size microstructure and precipitation strengthening produced yield strength and ultimate tensile strength increases of 27% and 8.5%, respectively. The homogenous grain size distribution had a more substantial effect on improving the mechanical properties than the annealing twin fraction.

Effects of annealing temperature on the microstructure, textures and tensile properties of cold-rolled Fe–13Cr–4Al alloys with different Nb contents

In this study, four Fe–13Cr–4Al alloys with different Nb contents (0–1.5 wt%) were prepared by using vacuum induction melting, forging, hot rolling, and cold rolling. The effects of annealing temperature (600 °C–1100 °C) and the Nb contents on the microstructure, textures as well as tensile properties were investigated. The dispersion of fine Fe2Nb-type Laves phase particles was observed in the BCC matrix and along grain boundaries. These particles effectively pinned dislocations and boundaries, resulting in stabilizing the microstructure, delaying the recrystallization temperatures and refining the recrystallized grains. The Laves phase particles were also able to retard the nucleation and growth of the γ fiber grains, therefore Nb-containing alloys had weak recrystallized γ fibers, which was beneficial to improve the processing properties of Fe–13Cr–4Al alloys. As the annealing temperature increased, the strengths decreased while the elongation increased. Because of the effects of solid solution strengthening, precipitation strengthening and fine grain strengthening produced by the addition of Nb element, the strength and hardness of the alloys increased with the increase of Nb content. Comprehensively considering the microstructure and mechanical properties, the suitable addition of Nb content was 1 wt%, and the optimum annealing treatment after cold-rolling with 50% thickness reduction was at 700 °C for 30 min.

Effect of Nb, Si and Cu on the crystallization process and magnetic properties of FeNbBP alloys

The effect of Nb, Si and Cu on crystallization process and magnetic properties of the Fe84Nb1B5P9M1 (M = Nb, Si, Cu) alloys were investigated. The experimental results show that the substitution of P by Nb, Si, or Cu leads to a wider interval between two crystallization exothermic peaks in comparison to that of the Fe84Nb1B5P10 alloy. The addition of Cu decreases the primary crystallization temperature (Tx1) of alloys while the doping with Si increases the Tx1 slightly. It is clear that the secondary crystallization temperature (Tx2) increases with the substitution of P by Nb, Si and Cu. Among the three elements, Nb has the largest effect on the precipitation of Fe(B,P) phases, which is due to the large negative mixing enthalpy of Nb and B, P. Based on the measurement of apparent activation energy, it is found that the shift in secondary crystallization peak to higher temperature is mainly due to the decrease in P content. After optimum annealing treatment, the Fe84Nb1B5P9M1 alloys show magnetic flux density above 1.7 T and coercivity below 10 A/m, which is better than Fe84Nb1B5P10 alloy.

Excellent soft magnetic Fe-Co-B-based amorphous alloys with extremely high saturation magnetization above 1.85 T and low coercivity below 3 A/m

Abstract Extremely good soft magnetic properties of high saturation magnetization ( B s ) above 1.8 T and low coercivity ( H c ) below 5 A/m were obtained for (Fe 1- x Co x ) 83 B 16 Si 1 ( x = 0.1–0.3) amorphous ribbons annealed at the temperature between T x1 -120 K and T x1 -40 K. Here T x1 is the onset temperature of the first exothermic crystallization peak. The best characteristics were 1.86 T for B s and 3 A/m for H c at x = 0.2. There are no previous data on the melt-spun alloys with high B s above 1.8 T and low H c below 5 A/m and hence the present amorphous alloys are regarded as a novel good soft magnetic alloy with high B s comparable to Fe-Si steels. Curie temperature ( T c ) of the x = 0.2 alloy was above T x1 (708 K), implying high thermal stability of magnetic characteristics. The saturated magnetostriction for x = 0.2 was about 32 ppm and the effective permeability at 1 kHz showed as high as 1.6 × 10 4 . The high B s can be attributed to the low metalloid content containing mainly B element which suppresses effectively the reductions of B s and T c among metalloid elements, as well as the optimum Co/Fe content ratio with the maximum magnetic interaction in conjunction with maximum atomic volume. Moreover, these alloy ribbons exhibited good bending ductility even after optimum annealing treatment, in addition to high Vickers hardness of about 1000 and improved corrosion resistance comparing with the corresponding Co-free alloy. The excellent soft magnetic amorphous alloys are promising for further extension as engineering soft magnetic materials.

The Microstructures and Electrical Resistivity of (Al, Cr, Ti)FeCoNiOxHigh-Entropy Alloy Oxide Thin Films

The (Al, Cr, Ti)FeCoNi alloy thin films were deposited by PVD and using the equimolar targets with same compositions from the concept of high-entropy alloys. The thin films became metal oxide films after annealing at vacuum furnace for a period; and the resistivity of these thin films decreased sharply. After optimum annealing treatment, the lowest resistivity of the FeCoNiOx, CrFeCoNiOx, AlFeCoNiOx, and TiFeCoNiOxfilms was 22, 42, 18, and 35 μΩ-cm, respectively. This value is close to that of most of the metallic alloys. This phenomenon was caused by delaminating of the alloy oxide thin films because the oxidation was from the surfaces of the thin films. The low resistivity of these oxide films was contributed to the nonfully oxidized elements in the bottom layers and also vanishing of the defects during annealing.

Forming limits of Mg alloy ZEK100 sheet in preform annealing process

Preform annealing (PFA) is a new two-stage forming technology with an intermediate annealing step, which extends the formability of light-weight (Al and Mg) alloys that comparable to deep drawing steels. ZEK100 is the only rare-earth containing magnesium sheet alloy that available commercially. The objective of this research is to understand the effect of preform and anneal on the forming limits of ZEK100. Various pre-strain paths and levels were introduced in the preform step followed by an optimum annealing treatment. The total strain-based forming limits of the PFA material are strongly dependent on the pre-strain level and annealing conditions. Based on the strain energy principle, an equivalent strain is employed to evaluate the effects of the pre-strain and anneal on the total limit equivalent strain of the PFA material, which is fitted as a function of the equivalent pre-strain and strain ratio of major strain to minor strain; and there is a critical equivalent pre-strain that leads to the lowest total limit equivalent strain at all strain ratios. Based on this concept, a new forming limit diagram (FLD) is constructed with the equivalent strain and the strain ratio as the horizontal and vertical axes, respectively, to evaluate the formability of Mg sheet in this two-stage forming process with intermediate annealing.

The soft magnetic properties of ring-shaped (Co0.6Fe0.3Ni0.1)68(B0.811Si0.189)27Nb5 bulk metallic glasses

Ring-shaped (Co0.6Fe0.3Ni0.1)68(B0.811Si0.189)27Nb5 bulk samples with an outer diameter of 10 mm, an inner diameter of 6 mm, and a thickness of 1 mm were successfully prepared by copper mold casting. The effects of annealing treatments on magnetic properties of the ring-shaped bulk sample were investigated. After the optimum annealing treatment, the resulting ring-shaped bulk sample exhibits good magnetic properties, i.e., low coercive force of 0.55 A/m, high maximum permeability of 433 000, and high permeability of 19 400 at 50 Hz under an AC field amplitude of 1.2 A/m, respectively. In addition, the ring-shaped bulk sample also shows low core loss of 0.09 W/kg at 50 Hz under induction of 0.5 T. The synthesis of ring-shaped bulk samples with good magnetic properties is encouraging for their potential applications as functional materials in the future.

Optimization of the Annealing Parameters for Improved Tensile Properties in Cold Drawn 0.12 wt% C Steel

Drawn low carbon steel is characterized by brittle fracture. These defects are associated with the poor ductility and high strain hardening due to the cold work. There is a need therefore to determine optimum heat treatment parameters that could ensure improved toughness and ductility. Determining the optimum annealing parameters ensures valued recrystallization and also minimizes grain growth that could be detrimental to the resulting product. 40% and 55% cold drawn steels were annealed at temperatures 500℃ to 650℃ at intervals of 50℃ and soaked for 10 to 60 minutes at interval of 10 minutes to identify the temperature range and soaking time where optimum combination of properties could be obtained. Tensile test and impact toughness experiments were done to determine the required properties of the steel. Polynomial regression analysis was used to fit the properties relationship with soaking time and temperatures and the classical optimization technique was used to determine the minimum soaking time and temperature required for improved properties of the steel. Annealing treatment at 588℃ for 11 minutes at grain size of 44.7 mm can be considered to be the optimum annealing treatment for the 40% cold drawn 0.12 wt% C steel and 539℃ for 17 minutes at grain size of 19.5 mm for the 55% cold drawn 0.12 wt% C steel.

Role of Si in high Bs and low core-loss Fe85.2B10−XP4Cu0.8SiX nano-crystalline alloys

The effects of Si element on structural and magnetic properties of Fe-rich Fe85.2B10−XP4Cu0.8SiX (x = 0–2.5 at. %) alloys were investigated. Our results show that addition of Si significantly reduces the activation energy for nucleation of α-Fe and increases the activation energy for grain growth. As a result, it is much easier to obtain a finer and uniform nanogranular structure (grain size ∼18 nm) made from densely packed α-Fe grains after annealing in the case of Si-containing alloys (Fe-B-P-Si-Cu) in comparison to Si-free alloys (Fe-B-P-Cu). However, addition of Si on the expense of B reduces the amorphous forming ability of the alloy, which results in lower reproducibility. The reproducibility improves significantly in Si-free alloy, but the structure of the alloy is relatively unstable on annealing, which means more strict annealing treatment is required. After optimum annealing treatment, Si-free alloys (Hc ∼ 6 A/m, Js ∼ 1.83 T) show superior soft magnetic properties than the Si-containing alloys (Hc ∼ 10 A/m, Js ∼ 1.78 T). Results show that the excellent soft magnetic cores can be obtained only if the extra heat generated on nano-crystallization of as-quenched amorphous phase can be released efficiently. The toroidal core of Si-free alloy (core-loss, W ∼ 0.58 W/kg at ∼1.7 T, 50 Hz) exhibits lower magnetic core loss than the Si containing alloys (core-loss, W ∼ 1.51 W/kg at ∼1.7 T, 50 Hz).

Soft magnetic properties of bulk FeCoMoPCBSi glassy core prepared by copper mold casting

Bulk Fe66Co10Mo3.5P10C4B4Si2.5 glassy core of 10 mm in outer diameter, 6 mm in inner diameter, and 1 mm in thickness was successfully prepared by copper mold casting. The effects of annealing treatments on magnetic properties and microstructure of these cores were investigated. After an optimum annealing treatment, the resulting bulk glassy core exhibits good magnetic properties, i.e., high saturation magnetic flux density of 1.23 T, low coercive force of 1.0 A/m, high maximum permeability of 450 000, respectively. In addition, the glassy core also shows low core loss of 0.4 W/kg at 50 Hz and at maximum magnetic flux density of 1 T. The synthesis of bulk glassy core with excellent magnetic properties is encouraging for enlarging the application field of ferromagnetic bulk glassy alloys.

Enhancement of coercivity for Nd-Fe-B thin films by the infiltration of Nd-Cu alloy cap layer

In order to understand the mechanism of coercivity (Hc) of Nd-Fe-B magnets, we have investigated the effect of thermal annealing treatment on Nd-Fe-B thin films with Nd-Cu alloy cap layers. A substantial enhancement of Hc from 19.0 kOe (1512 kAm−1) to 26.1 kOe (2078 kAm−1) was obtained for the Nd-Fe-B/Nd36Cu64 films after post-annealing at 400 °C. Through electron microscope observation, it was revealed that Nd and Cu enrichment is clearly observed in the grain boundary of the Nd-Fe-B layer, whereas the concentration of Fe was decreased there. These results suggest that the exchange coupling between Nd2Fe14B grains is weakened by the infiltration of a non-magnetic element into the grain boundary after the optimum thermal annealing treatment.

Effect of yttrium substitution on magnetic properties and microstructure of Nd-Y-Fe-B nanocomposite magnets

The phase evolution, microstructure and magnetic properties of Nd 9– x Y x Fe 72Ti 2Zr 2B 15 ( x=0, 0.5, 1, 2) nanocomposite ribbons were investigated. It was found that substitution of Y enhanced glass forming ability of the over-quenched ribbons and stabilized the amorphous phase during post annealing treatment. Appropriate content of Y substitution effectively refined the microstructure and enhanced the remanence of the annealed samples. The residual amorphous intergranular phase in the annealed sample improved the squareness of loops, resulting in enhanced maximum energy product. The optimum annealing treatment significantly improved magnetic properties of the Y substituted ribbons. Best magnetic properties, J r=0.78 T, H ci=923.4 kA/m, ( BH) max=98.5 kJ/m 3 were obtained from Nd 8YFe 72Ti 2Zr 2B 15 ribbon spun at V s = 4 m/s, and annealed at 700 °C for 10 min.

Optimization of annealing treatment parameters in a twin roll cast and warm rolled ZK60 alloy sheet

The microstructure of twin roll cast and warm rolled ZK60 alloy sheet was investigated using OM and TEM technique after annealing treatment at the temperature ranging from 300°C to 400°C. Tensile test at room temperature was performed to show the influence of annealing treatment on mechanical properties. Static recrystallization (SRX) was observed during annealing treatment of ZK60 alloy sheet at and above 300°C. Shear bands, dislocations and twins play an important role during static recrystallization and serve as nucleation sites. Disc-shaped precipitates could be found in annealed ZK60 alloy sheet. Higher temperature annealing treatment resulted in higher density precipitates, and at this condition the dispersion strengthening particles improved the ability of resistance to softening at elevated temperature. Annealing treatment at 375°C for 103s can be considered to be the optimum annealing treatment, and under this condition the tensile strength, yield strength and elongation are 388MPa, 301MPa and 22.9%, respectively.

Optimization of Annealing Treatment Parameters in a Twin Roll Cast and Warm Rolled Mg-4.5Al-1.0Zn Alloy

The microstructure of a twin roll cast (designated as TRC in short) and warm rolled Mg-4.5Al-1.0Zn (designated as AZ41 in short) alloy was investigated using OM and TEM after annealing treatment at the temperature range of 300oC~400oC. Tensile test was performed to show the influence of the annealing treatment on mechanical properties. The microstructure of AZ41 alloy sheet consisted of fibrous structure of elongated grains and shear bands along the rolling direction. Static recrystallization (SRX) was observed at and above 300oC during annealing treatment process. Shear bands, dislocations and twins play an important role during SRX and serve as nucleation sites, this leads to grain refinement. The sheet had higher strength and lower elongation after warm rolling. However annealing treatment after warm rolling induced the decrease of strength and increase of elongation. This results in the balance of strength and elongation in AZ41 alloy sheet. Annealing treatment at 400oC for 40min can be considered to be the optimum annealing treatment, and at this condition the tensile strength, yield strength and elongation are 375MPa, 285MPa and 17.7%, respectively.

Effects of post-annealing temperature on structural, optical, and electrical properties of ZnO and Zn1−xMgxO films by reactive RF magnetron sputtering

ZnO and Zn1−xMgxO thin films were deposited on (0001) sapphire substrates by a reactive RF magnetron sputtering. The effect of post-annealing temperature on structural, optical, and electrical properties was investigated over the annealing temperatures from 400 to 800°C. The crystallinity of ZnO film grown at 600°C was significantly improved by annealing treatment while the film grown at 700°C showed little improvement with annealing. The near band edge emission peak of ZnO films grown at 600 and 700°C appeared at 3.26eV after thermal annealing, which was not observable in as-grown film. The ratio of near band edge emission intensity to deep level emission intensity increased with annealing temperatures below 700°C but thereafter decreased. The optical transmittance in the visible region was not influenced much by annealing treatment, showing around 85% for both as-grown and annealed films. The annealed ZnO films exhibited an n-type characteristics whereas high insulator characteristics were observed for as-grown samples. The superior carrier concentration, mobility, and resistivity were achieved with an annealing treatment. An optimum annealing treatment was found to be at 600°C. The ZnO film grown at 600°C followed by the optimum post annealing shows the most improved structural, optical, and electrical properties even better than those of the film grown at a higher growth temperature (700°C) with post-annealing. With Mg doping into ZnO film, blue shift of 150–200meV was observed, depending on the annealing temperature. The reactive RF magnetron sputtering coupled with an optimum annealing treatment would provide a promising and economically feasible method for optoelectronic device fabrication.

Preparation, dosimetric characterisation and investigation of related TSL defect centres in Li3Po4:Mg,Cu phosphor.

L3PO4:Mg,Cu, a low effective atomic number and high sensitivity TSL phosphor, has been prepared. Its TSL glow curve shows a major peak around 360 degrees C with minor peaks around 110 degrees C and 230 degrees C. The optimum concentrations of the dopants are found to be 200 ppm each. Its gamma sensitivity is 1.2 times as compared to CaSO4:Dy (0.1 mol%). The optimum preirradiation annealing treatment is found to be 650 degrees C, 15 min. Its PL emission shows a band at 370 nm with excitation band at 250 nm. Dose to TSL response shows that its response is linear up to the gamma dose of 100 Gy for irradiations carried out at RT. An irradiated sample shows a distinct new ESR signal, which is tentatively assigned to an electron/hole localised on one of the oxygen(s) of the phosphate group. Step annealing experiments show decay of the defect centre around 340 degrees C. This correlates well with the TSL peak around 360 degrees C.

Crystallization and hard magnetic properties of Fe–Co–Nd–Dy–B amorphous alloys with glass transition

Glass transition followed by a supercooled liquid region was observed in the composition range of 4–56 at. %Co, 2–4.5 %Nd, 0–1.25 %Dy, and 18–30 %B in melt-spun Fe–Co–Nd–Dy–B amorphous alloys. The largest value in the supercooled liquid region (ΔTx) was 45 K for Fe66.5Co9.5Nd3.5Dy0.5B20. The crystallized structure consists of 2:14:1, Fe3B, and α-(Fe, Co) phases and their grain sizes after annealing for 420 s at 933 K are 15, 15, and 50 nm, respectively. The interparticle spacing of the 2:14:1 phase is less than 50 nm. The remanence (Br), coercivity (iHc), and maximum energy product (BH)max after an optimum annealing treatment (933 K, 420 s) are 1.24 T, 263 kA/m, and 92 kJ/m3, respectively, for the Fe66.5Co9.5Nd3.5Dy0.5B20 alloy. The rather good hard magnetic properties are interpreted to result from the exchange magnetic coupling among 2:14:1, Fe3B, and α-(Fe, Co) phases. The good hard magnetic properties in the crystallized state of the Fe–Co–Nd–Dy–B amorphous alloys with large ΔTx over 40 K are expected to enable the future fabrication of a bulk hard magnetic material by the simple process of the formation of a bulk amorphous alloy followed by optimum crystallization.

Synthesis of Fe&amp;ndash;Co&amp;ndash;Nd&amp;ndash;B Amorphous Alloys with Glass Transition and their Crystallization-Induced Hard Magnetic Properties

The glass transition followed by a supercooled liquid region was observed in the composition range of 5 to 57%Co, 2 to 4%Nd and 18 to 30 at%B in melt-spun Fe-Co-Nd-B amorphous alloys. The largest value of the supercooled liquid region defined by the difference between the glass transition temperature (T g ) and the crystallization temperature (T,), Δ T x (= T x - T g ), was 40 K for Fe 66.5 Co 10 Nd 3.5 B 20 and the T g and T x values are 802 K and 842 K, respectively. The crystallized structure consists of Fe 3 B, Nd 2 Fe 14 B, α-Fe and Nd 2 Fe 23 B 3 phases and their grain sizes after annealing for 420 s at 933 K are 20, 20, 70 and 10 nm, respectively. The interparticle spacing of the Nd 2 Fe 14 B phase are evaluated to be less than 50 nm for the 10%Co alloy. The magnetization at an applied field of 1256 kA/m (I 1256 ), remanence (B r ), intrinsic coercive force (iH c ) and maximum energy product (BH) max of the Fe 66.5 Co 10 Nd 3.5 B 20 alloy subjected to an optimum annealing treatment (933 K, 420 s) are 1.46 T, 1.25 T, 187 kA/m and 86 kJ/m 3 , respectively. The rather good hard magnetic properties are interpreted to result from the exchange magnetic coupling among Nd 2 Fe 14 B, Fe 3 B and α-Fe phases. The achievement of the rather good hard magnetic properties in the crystallized state of the Fe 66.5 Co 10 Nd 3.5 B 20 amorphous alloy with the large ΔT x of 40 K is expected to enable the future fabrication of a bulk hard magnetic material by the simple process of the formation of a bulk amorphous alloy followed by optimum crystallization.