Phase Refinement Research Articles

Effect of Friction Stir Processing on the Microstructure, Damping Capacity, and Mechanical Properties of Al-Si Alloy

Friction stir processing (FSP) was conducted on an Al-Si casting alloy. The Si phase and Al grains of an Al-Si casting alloy were refined through FSP. Furthermore, FSP with high rotation rate led to the precipitation of Mg and Si atoms and the formation of Mg2Si phase in the Al-Si alloy. Precipitation improved the low-strain damping capacity but deteriorates high-strain damping capacity of the FSP sample at room temperature. At low rotation rate, the FSP sample exhibited excellent high-temperature damping capacity mainly because of its fine grain structure and the low density of its pinning points. The plastic instability of the Al-Si alloy was eliminated by FSP because of the refinement of the Si phase. The increase in the strength of each FSP sample was attributed to the increase in second-phase and boundary strengthening effects. Thus, the mechanical properties and damping capacity of Al-Si were enhanced after FSP.

Designing the composition and processing route of aluminum alloys using CALPHAD: Case studies

Aluminum alloys have been widely used in various industries, and continuous improvement in the properties of these alloys is required to meet consumer demand for high-performance devices. This review introduces five recent case studies where the CALPHAD method was applied in the development of high-performance Al alloys. CALPHAD calculations can reasonably predict the solidification microstructure of the Al-7Si-2Cu-1Mg alloy and 4343/3527/4343 brazing sheets, although, some deviations are caused by solid-state diffusion occurring during the actual solidification process. CALPHAD is useful for predicting the complex solidification behavior of Al-(12-18)Si piston alloys and Al-6Mg-9Si-10Cu-10Zn-3Ni natural composites, and the precipitation behavior of the Al matrix. The application of CALPHAD can also provide valuable information on the properties of Al alloys, such as that on the erosion of brazing sheets, fluidity of alloy melts, and refinement of secondary phases by melt treatment.

Particle Distribution and Mechanical Properties of Nano-SiC<sub>P</sub>/Al-Cu Composites

Generally it is difficult to disperse nanosized particles uniformly in metal matrix. In this paper nanoSiC particles reinforced Al-5%Cu matrix composites were prepared by molten-metal process, combined with high energy ball-milling and ultrasonic vibration methods. Ultrasonic vibration treatment (UV) has been successfully used to disperse the particles distribution of nanoSiCp particles in the matrix. Big aggregates of particles are eliminated by the effects of cavitation and the acoustic streaming of UV for 1 min. All the particles aggregates are eliminated and the particles are uniformly distributed in the melt after treated by UV for 5 min. The refinement of Al2Cu phase in Al-Cu alloy is more obvious and more uniform distributed with the increase of UV time. The ultimate tensile strength (UTS), yield strength and elongation of the 1wt% nanosized SiCp/Al-5Cu composites treated by UV for 5 min are increased by 37%, 9.5% and 270% respectively, compared with the untreated composites.

TMP as an Effective Technique to Produce Ultra-Fine Grained Steels

In recent years, great attention is paid to the creation of methods andthe technological processes providing ultrafine-grained state of metal materials including submicro - and nanocrystalline ones. It pertains to structural components and to the phases constituting the particular metal or alloy. The main development in terms of obtaining bulk metallic materials received in recent years, various schemes of processing of metals by plastic deformation, which allows to realize the so-called severe plastic deformation (SPD). Such approach usually propose realization of large plastic strains, providing a well-developed fragmented substructure with the creation of high angle misorientation of the boundaries between the fragments of the substructure. The second direction in receiving finely divided state is to create technologies that provide a significant refinement of phase as a result of processing. The most effective way of achieving both the above effects applied to bulk metallic materials is Thermomechanical Processing (TMP), which can be used as a standalone technology or in combination of such methods as accumulation roll bonding (ARB) or other similar SPD methods. This paper discusses various methods of thermomechanical processing, based on the use of hot, warm and cold deformation, in various combinations applied to single and multiphase steels, ensuring the achievement of ultra-fine grained structure with elements of submicro - and nanostructures.

Effect of Trace Yttrium Addition and Heat Treatment on the Microstructure and Mechanical Properties of As-Cast ADC12 Aluminum Alloy

The effects of rare earth yttrium (Y) additions and the heat treatment process on the microstructure and mechanical properties of as-cast ADC12 aluminum alloy have been investigated. The results showed that the primary Si crystals were significantly refined from long axis to fibrous or granular when the Y content was 0.2 wt%. Compared to the matrix, the mean area and aspect ratio were decreased by 92% and 75%, respectively. Moreover, the Si and Fe-rich phases were spheroidized and refined with a small average size during the solid solution. It was also noted that the copper-rich phases were dissolved into the matrix. Correspondingly, it was found that after metamorphic and heat treatment the ultimate tensile strength (UTS), elongation, and, hardness increased by 81.9%, 69.7%, and 74.8%, respectively, compared to the matrix. The improved mechanical properties can primarily be attributed to the optimization of the microstructure and the refinement of various phases.

Microstructure and Mechanical Characterization of Friction-Stir-Welded 316L Austenitic Stainless Steels

Fusion welding of austenitic stainless steels (ASSs) causes undesirable metallographic changes. An attempt has been made to join 3-mm-thick 316L ASS plates using friction stir welding and correlate the microstructural evolution and the mechanical properties under various welding conditions. Tungsten alloy (W-Re) tool was employed for welding. Successful joints were obtained within a range of traverse speeds (45-85 mm/min) used in this work. Various zones were observed across the joint line. The stir zone exhibited considerable grain refinement and traces of delta ferrite phase. EBSD images showed a decreasing grain size with increased traverse speed. XRD patterns and TEM images confirmed the existence of delta ferrite. The mechanical properties of the joints including microhardness, tensile strength, impact toughness and bending were further reported.

Microstructure and elevated temperature mechanical properties of a direct-chill cast AA4032 alloy with copper and erbium additions

Billets from an AA4032 alloy are usually produced by direct-chill (DC) casting to subsequently manufacture piston components by hot forging process. This work presents the effect of combined copper (Cu) and erbium (Er) addition on microstructure, mechanical properties and thermal expansion of an AA4032 alloy at room and elevated temperatures. Metallographic examination of samples was carried out to characterize the eutectic refinement, primary Si particles and second phase formation at different levels of Cu and Er additions. The results revealed that the amount of primary Si particles increased with increasing Cu addition from 1% to 3.5%. This indicated that Cu addition shifted the eutectic point in the alloy system. However, the Er addition resulted in complete elimination of primary Si particles and refinement of eutectic silicon phases. These results were supported by Thermo-Calc calculations. With increasing Cu and Er concentration to 3.5% and 0.4%, respectively, the hardness increased from 116 HB to 144 HB. The ultimate tensile strength (UTS), yield strength (YS) and elongation (El) were investigated at both room and elevated temperatures. At room temperature, the UTS of these alloys were enhanced with Cu and Er alloying from 279 MPa to 312 MPa. At 350 °C, the UTS was improved to 117 MPa while El was maintained at about 22%. This indicated that Er addition was effective in optimizing the high-temperature properties. The tensile fracture surfaces of the specimens showed that the main failure mechanism was predominantly due to the cracking of primary Si particles in the Al matrix, resulting in the brittle fracture of the alloys without Er. The fracture surface of the samples with Er addition displayed the path through the refined eutectic phase in the ductile fracture mode. The coefficient of linear thermal expansion (CTE) decreased to about 18.3 × 10−6 K−1 at high operating temperature (100–350 °C) for the Er containing alloy. Therefore, this study suggests that the combination of Cu and Er additions in an AA4032 alloy controls the beneficial microstructure in terms of primary Si particles, the refined eutectic Si phase and secondary phases in the Al matrix, which improves mechanical and thermal performances. The low coefficient of linear thermal expansion (CTE) of this alloy makes it suitable for elevated temperature applications.

Effects of adding nano-CeO2 powder on microstructure and hydrogen storage performances of mechanical alloyed Mg90Al10 alloy

For pushing Mg-based alloys developing to the practical applications, nano-CeO2 powders were added into the mechanical alloyed (MA) Mg90Al10 alloy. The aim of it is to improve the thermodynamics and kinetics through generating new intermetallic compound, reducing the grain size and increasing the solid solubility of Al in Mg. XRD analysis showed that adding nano-CeO2 powder causes the generation of Mg17Al12 phase and grain refinement of the MA Mg90Al10 + x wt% CeO2 (x = 1, 3, 5 and 8) composites. It also increases the solid solubility of Al in Mg, while results in the reduction of Mg lattice volume. The dehydrogenation enthalpy (ΔHde), calculated from Van't Hoff equation, is reduced from 75.43 kJ mol−1 H2 for the MA Mg90Al10 alloy to 74.22, 72.70, 70.28 and 73.71 kJ mol−1 H2 for the MA Mg90Al10 + x wt% CeO2 (x = 1, 3, 5 and 8) composites, respectively. The increased grain boundaries, caused by the grain refinement and formation of the mutilphase structure, are beneficial to reduce the dehydrogenation activation energy (Ede(a)). It is obtained through Johnson-Mehl-Avrami-Kolmogorov model, which is 162.06, 121.86, 103.73, 101.83 and 109.08 kJ mol−1 H2 for the MA Mg90Al10 + x wt% CeO2 (x = 0, 1, 3, 5 and 8) composites, respectively.

Effects of an Alternating Magnetic Field/Ag Multi-Alloying Combined Solidification Process on Cu⁻14Fe Alloy.

An alternating magnetic field (AMF)/Ag multi-alloying combined process was applied to the solidification of Cu–14Fe alloy to study its effects on the microstructure and properties of the resulting samples. The applied AMF and Ag multi-alloying had positive effects on the refinement of the primary Fe phase and precipitation of Fe solute atoms, respectively. These results indicated that the combined AMF/Ag multi-alloying process was effective to improve the distribution of the primary Fe phase and reduce the Fe content of the Cu matrix, which increased the conductivity of the alloy. The application of the combined AMF/Ag multi-alloying process to the solidification of Cu–Fe alloy provided samples with improved comprehensive properties compared with those of samples solidified using a single process (AMF or Ag multi-alloying).

Multistage cryogenic treatment of X153CrMoV12 cold work steel

The article presents the influence of multistage cryogenic treatment (MCT) on the microstructure and properties of X153CrMoV12 cold work steel. Basic mechanical properties of steel, such as hardness and wear resistance (3 rolls-cone system) were tested. The microstructure of steel was observed by means of scanning microscopy. Test results were compared with the properties of steel subjected to conventional heat treatment and deep cryogenic treatment (DCT). The cryogenic processes of X153CrMoV12 steel influenced on the percentage of strengthening phases in the material matrix microstructure. In the case of MCT and DCT, similar changes in the microstructure were observed, consisting in increasing of the amount, more uniform distribution and refinement of carbide phases. Changes in the microstructure of steel affected the mechanical properties of the material.

Effect of grain refinement and crystallographic texture produced by friction stir processing on the biodegradation behavior of a Mg-Nd-Zn alloy

The application of a single pass of friction stir processing (FSP) to Mg-Nd-Zn alloy resulted in grain refinement, texture evolution and redistribution of second phases, which improved corrosion resistance. In this work, an as-rolled Mg-Nd-Zn alloy was subjected to FSP. The microstructure in the processed zone of the FS-400 rpm alloy exhibited refined grains, a more homogenous grain size distribution, less second phases, and stronger basal plane texture. The corrosion behavior assessed using immersion tests and electrochemical tests in Hank￢??s solution indicated that the FS-400 rpm alloy had a lower corrosion rate, which was attributed to the increase of basal plane intensity and grain refinement. The hardness was lowered slightly and the elongation was increased, which might be attributed to the redistribution of the crushed second phases.

Optimization of processing parameters and establishment of a relationship between microstructure and mechanical properties of SLM titanium alloy

The processing parameters of a selective laser-melted (SLM) Ti6Al4V alloy were systematically optimized for optimal surface roughness and relative density. The relationship between microstructure and mechanical properties were established in the optimal parameter range. The results showed that the optimal laser power and scan speed was 200–250 W and 850–1150 mm/s, respectively. The laser power and scan speed played contradicting roles in the resultant roughness and porosity. An appropriate increase in laser power and decrease in scan speed could reduce the surface roughness and simultaneously improve the density and dimensional accuracy. When the laser power was 200 W, the microstructure varied from equiaxed grains to mixed equiaxed-columnar grains, and then it varied to columnar grains as the scan speed changed from 250 mm/s to 850–1750 mm/s. The acicular structure inside the grains transformed from an α (α′) + β phase to an α′ (α) phase with gradual grain refinement. Some nano-β phase precipitated near the acicular phase. Micro-hardness measurements revealed different values at the top, middle and bottom of the samples with increasing laser power and showed a reduced hardness gap with increasing scan speed. However, the elongation continuously increased with increasing scan speed and reached a maximum value of 7.8% at a scanning speed of 1150 mm/s. Decrease in elongation was observed when the laser power increased to 275 W. These variations in the hardness and mechanical properties were attributed to the combined effects of nano-β phase and grain refinement of acicular α (α′) martensites.

Microstructure evolution, mechanical properties and strengthening mechanism of refractory high-entropy alloy matrix composites with addition of TaC

This study focuses on novel refractory MoNbRe0.5W(TaC)x high-entropy alloy matrix composites synthesized by vacuum arc melting. The microstructure evolution, compressive mechanical properties at room temperature and strengthening mechanism of the composites with addition of TaC are analyzed and discussed. The MoNbRe0.5W(TaC)x composites consist of a BCC solid solution as the matrix and an eutectic microstructure (BCC and multi-component carbide (Mo, Nb, W, Ta)C phases) at grain boundaries. The lamellar eutectic structure would be formed from the decomposition of subcarbide (Mo, Nb, W, Ta)2C and the fully solid solubility of Re. The MoNbRe0.5W(TaC)0.5 composite has the maximum failure strain of 10.25%. The MoNbRe0.5W(TaC)0.5 to MoNbRe0.5W(TaC)0.6 composites exhibit excellent comprehensive mechanical properties, with excellent strength and reasonable ductility at room temperature. The reinforcement mechanism of the composites is dominated by precipitation and fine-grained strengthening effect. The good ductility of MoNbRe0.5W(TaC)0.5 composite is contributed to the grain refinement of the BCC matrix phase.

Al-1.5Fe-xLa Alloys for Lithium-Ion Battery Package

Al foil with high formability and corrosion resistance is highly desired for lithium-ion battery soft packaging. Annealing treatment has a significant impact on the performance of soft packaging Al foil. The effects of both La content and the annealing temperature on the microstructure, mechanical properties, and corrosion behavior of Al-1.5Fe-La alloy was investigated through optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), tensile testing, potentiodynamic polarization testing, and electrochemical impedance spectroscopy (EIS) testing. A higher addition of La resulted in the formation of AlFeLa particles and a refinement of the Fe-rich second phase. The Al-1.5Fe-0.25La alloy had a higher formability and corrosion resistance than the Al-1.5Fe-0.1La alloy. Microstructure analysis indicated that recovery, recrystallization, and grain growth successively occurred in the Al-Fe-La alloy with the increase of the annealing temperature from 200 °C to 250 and 380 °C. After annealing at 250 °C, the Al-Fe-La alloys had the highest corrosion resistance due to refined grain and a high fraction of small-angle grain boundaries.

CAB: a cyclic automatic model-building procedure.

The program Buccaneer, a well known fast and efficient automatic model-building program, is also a tool for phase refinement: indeed, input phases are used to calculate electron-density maps that are interpreted in terms of a molecular model, from which new phase estimates may be obtained. This specific property is shared by all other automatic model-building programs and allows their cyclic use, as is usually performed in other phase-refinement methods (for example electron-density modification techniques). Buccaneer has been included in a cyclic procedure, called CAB, aimed at increasing the rate of success of Buccaneer and the quality of the molecular models provided. CAB has been tested on 81 protein structures that were solved via molecular-replacement, anomalous dispersion and ab initio methods. The corresponding phases were submitted to a phase-refinement process that synergically combines current phase-refinement techniques and out-of-mainstream refinement methods [Burla et al. (2017), Acta Cryst. D73, 877-888]. The phases thus obtained were used as input for CAB. The experimental results were compared with those obtained by the sole use of Buccaneer: it is shown that CAB improves the Buccaneer results, both in completeness and in accuracy.

Effects of Amplitude of Die Vibration on Cast Structure of Al4.5Cu Alloy

The effect of mechanical vibration on structural evolution during gravity die casting of Al4.5Cu (LM11) alloy was studied. Two types of die were used to cast alloy, namely top gating die and bottom gating die. The preheated die was placed on a vibrating table prior to casting. The frequency of die vibration was 50 Hz. The amplitude of die vibration was varied to 0.5 mm, 0.75 mm, and 1.05 mm to understand the role of vibration on structural evolution. When vibration amplitude was increased to greater than 1.05 mm, it generated higher degree of turbulence which resulted in splashing of molten metal out of the die and consequently it was difficult to cast the alloy. For comparative purpose, castings were produced without vibrating the die. Microscopic examination showed progressive microstructural transformation from predominantly dendritic structure in casting without vibration to greater degree of globularized primary α-Al structure in casting produced with die vibration. In addition, casting produced in vibrating die showed microstructural refinement and reduction in microsegregation of Cu in the matrix. The average grain size of casting produced in the top gating die under vibration with 1.05 mm of amplitude at 50 Hz was 0.75 mm, whereas that of casting produced in stationary die was 2.1 mm. Further, vibration of die reduced the size of eutectic Al2Cu phase from 10.23 μm (without vibration) to 6.75 μm (with vibration at 50 Hz and amplitude of 1.05 mm). The refinement of grain and eutectic phase in castings produced under vibration is because it caused forced convection in melt that increased cooling rate during solidification. The evidence of high cooling rate in casting produced in vibrating die is noted from secondary dendritic arms spacing (SDAS) values. The SDAS value of casting produced in die vibrating at 50 Hz and 1.05 mm of amplitude was less as compared to that of casting produced in stationary die, and correspondingly the calculated cooling rate of casting produced in vibrating die was greater than that of casting produced in stationary die. Significant reduction in shrinkage porosity was observed in casting produced in vibrating die, and consequently their density was higher as compared to those produced without vibrating the die. This is attributed to the increase in melt flowability due to the fragmentation of primary α-Al dendrites to form higher amount of globularized microstructure and grain refinement during solidification of casting in vibrating die.

Effect of minor Nd substitution for Y on microstructure and corrosion resistance of extruded Mg–Zn–Y alloy

Abstract The influence of minor Nd substitution on the microstructure and corrosion resistance of Mg–Zn–Y alloy were investigated. Results indicate that the partial substitution of Nd for Y can effectively refine grains but deteriorate the corrosion resistance of extruded Mg–Zn–Y alloy. The corrosion rates, measured by immersion tests in 3.5% NaCl solution at 25°C, are 12 and 19 mm · y−1 for the Mg-5.6Zn-1.4Y and Mg-5.6Zn-1.0Y-0.4Nd alloys, respectively. The negative effect of Nd is associated with enhanced microgalvanic corrosion resulting from grain refinement and higher area of second phase, as well as to a degraded protectiveness of the corrosion product layer.

Structure response characteristics and surface nanocrystallization mechanism of alpha phase in Ti-6Al-4V subjected to high energy shot peening

Structure features and grain refinement of alpha phase in coarse-grained Ti-6Al-4V subjected to surface severe plastic deformation by using high energy shot peening (HESP) were investigated via high-resolution transmission electron microscope. The results illustrated the novel deformation-induced structure response characteristics, including markedly reduced contribution of twinning to deformation of coarse-grained alpha phase with hexagonal close-packed (hcp) structure, dramatical rise of pyramidal <c+a>-type dislocation density accompanying an increase in grain refinement level of alpha phase, and unusual phase transformation of alpha ultrafine grains (UFGs) from hcp to face-centered cubic (fcc) structure. Based on the above-mentioned results, nanocrystallization mechanism of alpha phase was obtained as follows. The massive dislocation tangles, dislocation bands and a handful of single-system tension twins were firstly generated and subdivided the original grains into elongated UFGs, and then transversely disintegrate elongated UFGs into equiaxed UFGs, which twinning was gradually replaced by pyramidal <c+a>-type dislocation slip during the above-mentioned process. Most of equiaxed UFGs with hcp structure subsequently underwent crystal rotation to transform into randomly-oriented equiaxed nanograins. Phase transformation from hcp to fcc structure occurred in a small amount of equiaxed UFGs, in which twin-twin and dislocation-twin interactions ultimately resulted in the formation of nanograins with fcc structure.

Study of the role of Ti doping on magnetic properties of some nanocomposite alloys of α-Fe/Nd2Fe14B type

• Proper Ti content can refine the microstructure and improve the exchange coupling interaction, leading to enhance the magnetic properties . • The optimum ( BH ) max (16.24 MGOe) is obtained with the Ti addition at x = 0.4. • The magnetization reversal behaviors were investigated by analyzing the recoil loops and the FORC diagrams. In the present work, the (Nd 0.8 Ce 0.2 ) 2 Fe 12 Co 2−x Ti x B (x = 0–0.6) permanent alloys are prepared by melt-spinning method. Ti addition has proved to result in relevant improvements in the microstructure and magnetic properties. The enhanced coercivity H cj of 7.13 kOe and maximum energy product ( BH ) max of 16.24 MGOe with a slight decrease in B r only have been obtained with the Ti content at x = 0.4. Microstructural observations reveal that the significant improvements of magnetic properties originate from the hard 2:14:1 magnetic phase refinement by introducing Ti element. The magnetization reversal behavior and energy loss characteristic have also been thoroughly investigated. The first-order reversal curves (FORCs) suggest that the Ti-doped sample with a higher maximum ρ of the major peak and the flat surface is responsible for the stronger inter-phase exchange coupling and better magnetic performance.

Laser surface modification of Mg-Zn-Gd alloy: microstructural, wettability and in vitro degradation aspects

Mg-Zn-Gd have great potential for biomedical applications owing to excellent bioactivity and non-toxicity properties. In the present study, laser surface melting (LSM) was carried out on newly developed Mg-1Zn -2Gd (wt%) alloy. Effects of laser energy on microstructural evolution, corrosion properties, surface energy, and hardness have been investigated. The surface modified sample processed at different energy densities showed fine grain structure in the melt zone compared to the untreated substrate. Grain refinement in the laser melted region improved the hardness by 60%. The surface roughness was found to be increased with increasing laser energy density. At higher energy density, removal of materials from the surface is enhanced, resulting in deeper grooves and higher surface roughness. The wettability studies indicated that the variations in surface geometry, grain size and surface roughness of LSM samples strongly influence the surface energy and hydrophilicity. Improved wetting of LSM sample was achieved owing to grain refinement and low surface roughness. The corrosion resistance determined by immersion and electrochemical methods of laser melted sample in Hank’s balanced salt solution improved considerably due to grain refinement, meltpool depth and uniform distribution of secondary phases.