Phase Refinement Research Articles

The evolution of long-period stacking ordered phase and its effect on dynamic recrystallization in Mg-Gd-Y-Zn-Zr alloy processed by repetitive upsetting-extrusion

Based on the repetitive upsetting-extrusion (RUE) process, the evolution of the LPSO phase and its effect on the dynamic recrystallization (DRX) of Mg-9Gd-4Y–2Zn-0.5Zr (wt%) alloy during the multi-pass deformation were studied. The results showed that with the increase of RUE processing, the DRX fraction gradually increased, the grains were effectively refined, and the texture was weakened. The lamellar LPSO phase mainly underwent mechanical crushing, bending, tearing, and kinking to become refinement. The block-shaped LPSO phases dissolved during the deformation process, forming a stripe-like structure, and its rest of the refinement mechanism was similar to the lamellar phase. The refinement of block-shaped phase was slower than that of lamellar phase. However, the block-shaped phases always promoted DRX through the PSN mechanism, while the lamellar phases with a large volume inhibited the generation of DRX. After the refinement of lamellar phases, the inhibition effect was transformed into the promotion effect, which leaded to a continuous increase in the DRX fraction. This further promoted the uniform distribution of the LPSO phases and obtained a more ideal microstructure.

G–D Map Method for Analyzing Effects of Elements on Size Control of In Situ Formed Mg2Si in Mg Melts

An approach for selecting alloying elements to control the size of an in situ formed phase is proposed based on a G–D map, which is derived from basic thermodynamic and kinetic principles. The G–D map is divided into four zones. Elements in Zone III are potential refiners whereas those in Zone II should be avoided in processing. When applied to the Mg2Si/Mg system, we find that Sr, P, Sb and Sn refine Mg2Si by increasing the nucleation rate and inhibiting the growth rate. Conversely, Ti, Mn, Zr and V contribute to coarse-shaped Mg2Si by postponing nucleation. The content of alloying elements should be matched with the Si content, and the required amount can be pre-estimated from the G–D map. Mg2Si formed in Mg-Al and Mg-Zn alloy is smaller than that in Mg-Si and Mg-Mn alloy, because Al and Zn suppress the diffusion of Si, particularly at high Si contents. The predictions of this approach are consistent with experimental observations. Hence, the G–D map can provide useful guidance for quantitative phase refinement design.

Microstructure Evolution and Properties Tailoring of Rheo-Extruded Al-Sc-Zr-Fe Conductor via Thermo-Mechanical Treatment.

Low-cost heat-resistant Al-Sc-Zr-Fe conductor wires were successfully manufactured by continuous rheo-extrusion process, and the mechanical and conductive properties of the materials were analyzed and compared after three different thermo-mechanical treatment methods. The coarse plate-shape Al3Fe phase transformed to small sized rod-like phase after solid solution treatment at 630 °C for 21 h. Direct aging treatment at 300 °C for 24 h led to the refinement and spheroidization of Al3Fe phase with a diameter of 200 nm. After the subsequent aging treatment at 300 °C for 24 h, the tensile strength and conductivity of the alloy wire significantly increased due to the homogeneous precipitation of the coherent spherical Al3(Sc, Zr) phase with an average size of 15 nm. The tensile strength, elongation, and conductivity of the alloy conductor wire after optimized thermo-mechanical treatment reached 165.7 MPa, 7.3%, and 60.26% International Annealed Copper Standard (IACS), respectively. The thermal resistance of the present alloy wire was superior to that of standard AT1 type alloy conductor according to IEC international standard.

Structure and property modulation of primary CoSn and peritectic CoSn2 intermetallic compounds through ultrasonicating liquid Sn–10%Co alloy

The effects of power ultrasound on the peritectic solidification of binary Sn–10%Co peritectic type alloy were investigated. If introducing ultrasound in the whole solidification process, primary CoSn intermetallic compound which grew as coarse strips with a preferred grain orientation under static condition was considerably refined and exhibited a random orientation distribution. Moreover, the significant increase in thickness ratio of peritectic CoSn2 to primary CoSn compounds indicated that the peritectic transformation was remarkably enhanced. To further reveal the underlying mechanism, power ultrasound was respectively applied to primary phase growth and peritectic transformation stages. As compared with the latter one, the former procedure led to a finer primary CoSn phase and a higher peritectic transformation extent. The results showed that ultrasound induced refinement of primary CoSn phase played the dominant role, while ultrasound accelerated atomic diffusion between primary and peritectic solid phases may also contributed to the enhancement of peritectic transformation. Both the yield strength and ultimate compressive strength of Sn–10%Co alloy were improved after ultrasonic solidification.

A novel rheological high pressure die-casting process for preparing large thin-walled Al–Si–Fe–Mg–Sr alloy with high heat conductivity, high plasticity and medium strength

An air-cooled stirring rod (ACSR) process for efficiently preparing large volumes of semisolid slurry was introduced. A new low-cost casting Al–Si–Fe–Mg–Sr alloy was used to prepare large thin-walled heat-dissipating shells using both conventional HPDC and ACSR rheological high pressure die-casting (Rheo-HPDC) technologies. Their microstructures, thermal conductivities, elevated temperature and room temperature mechanical properties, and corrosion behaviors were compared. Furthermore, this work analyzed the mechanisms responsible for the microstructure refinement and performance enhancement in ACSR Rheo-HPDC alloys. The results showed that only 25 s was needed to prepare 32 kg of the semisolid slurry using ACSR process. The alloy prepared by ACSR Rheo-HPDC generated a large number of fine spherical primary α-Al particles with a volume fraction greater than 40%. The Rheo-HPDC alloy showed a moderate strength, high plasticity, and high heat conductivity. The heat conductivity, ultimate tensile strength and elongation of the Rheo-HPDC alloy were 184 W/(m.K), 264 MPa and 12.2% respectively, while those of the HPDC alloy were 167 W/(m.K), 228 MPa and 5.8% respectively. The improvement of heat conductivity of the alloy formed via ACSR Rheo-HPDC was mainly ascribed to the decrease of electron scattering by the refinement of eutectic silicons and Fe-rich intermetallics. This allowed the electron flow to pass through the eutectic Si region more easily. The refined and uniformly-distributed heat-resistant β-Al5FeSi intermetallics effectively prevented grain boundary sliding, so the Rheo-HPDC alloy showed superior high-temperature mechanical properties. The Rheo-HPDC alloy presented a more excellent corrosion resistance to the conventional HPDC alloy due to the refinement of iron-rich phase and eutectic silicons and the reduction in the potential difference between the matrix and the iron-rich phase.

Effect of Ni and Mo contents on microstructure, magnetic and mechanical properties of Ti(C, N)-based cermets

Ti(C,N)-based cermets were prepared by vacuum sintering. The effect of Ni and Mo contents on microstructure, magnetic and mechanical properties of cermets were investigated using XRD, SEM, EDS, and VSM. The results showed that the proportion of ceramic hard phase decreased gradually, and the core-rim structure became incomplete with Ni content. However, with an increase in Mo content from 6 to 18 wt. %, the thickness of rim phase slightly increased. The complete core-rim structure refined the grain size of cermets, and the particles became the finest when Mo content was about 14 wt. %. The magnetization of cermets increased with Ni content, while their magnetization gradually weakened with Mo content. The deterioration of magnetic properties was caused by the high total content of Mo and Ti alloying elements in the binder phase. Meanwhile, the hardness of cermets decreased, while the TRS initially increased, followed by a gradual decrease with content of Ni. With an increase in Mo content, the hardness and TRS of Ti(C,N)-based cermets increased firstly and then decreased. The fracture toughness of cermets increased with Ni content, while the increasing Mo content reduced the fracture toughness. Due to grain refinement and solid-solution strengthening of the binder phase, the optimal composition of cermet was Ti(C,N)-14Mo-25Ni, whose hardness, TRS, and Kic values were ~90.3 HRA, 2340 MPa and 11.7 MPa·m1/2, respectively.

Effect of shot peening coverage on hydrogen embrittlement of a ferrite-pearlite steel

Effect of a wide range of shot peening (SP) coverage on hydrogen diffusion and hydrogen embrittlement (HE) of a steel consisting of ferrite and pearlite was investigated. Conventional SP (CSP) reduces diffusivity and HE because of increase of dislocation trapping sites. Although severe SP (SSP), which uses higher coverages than CSP, increases the area of ferrite grain boundaries as a result of grain refinement, it cannot suppress further the diffusion and HE, as it cannot induce a further evident increase in strong hydrogen trapping sites such as dislocations. However, when coverage is increased to so high that causes the breaking and refinement of pearlite phase, diffusion and HE is suppressed further, because the dispersed distribution of ultrafine pearlite particles within ferrite matrix provides more strong interface trapping sites. SP-induced change of trapping sites plays a more critical role in HE and diffusion, in comparison with induced residual compressive stresses.

Modeling and optimization of combustion synthesis for hydroxyapatite production

In this study, the combustion synthesis of hydroxyapatite was studied and optimized under controlled experimental conditions. The hydroxyapatite content, crystallinity and crystallite size were monitored under changes in type of fuel, pH or red/ox ratio, muffle temperature, and reaction time. The products were characterized by X-ray diffraction, refinement of crystalline phases by the Rietveld method, scanning electron microscopy, and infrared spectroscopy with the Fourier transform. The decomposition of hydroxyapatite, which was the major phase, produced beta tricalcium phosphate in all samples, as indicated by their diffractograms. Infrared spectroscopy analysis revealed the presence of b-type carbonate groups in the structure; thus, the synthesized compound has the following chemical formula: Ca10-x (PO4)6-x (CO3)x (OH)2-x, where 0 < x < 2, which corresponds to carbonated hydroxyapatite (CHAp). The combustion process was modeled using a first-degree polynomial, and we found that the interaction between time and temperature to be the most influential parameter. Optimization indicated that processing conditions at 650 °C for 30 min, using urea at pH = 2 and ϕe = 1.134, produced the best result in terms of HAp composition, yielding 89.25% wt.

Effect of Ultra-sonicated Y2BaCuO5 on Top-Seeded Melt Growth YBa2Cu3Oy Bulk Superconductor

In this work, we tried to improve the superconducting performance of bulk YBa2Cu3Oy (Y123) superconductors via Y2Ba1Cu1O5 (Y211) secondary phase refinement. A novel method of ultra-sonication was used to refine the Y211 secondary phase particles. The Y211 powder was treated by ultra-sonication for 0 to 80 min with steps of 20 min, keeping the power (300 W) and frequency (20 kHz) constant. For synthesis of the YBCO bulk, we employed top-seeded melt growth (TSMG) with Pt addition. Magnetization measurements showed a superconducting transition temperature at around 91 K, irrespective of ultra-sonication parameters. Interestingly, critical current density and trapped field were found to be proportional to the ultra-sonication duration. YBCO bulk sample (20 mm diameter, 7 mm in thickness) fabricated for 80 min ultra-sonicated Y211 showed a maximum trapped field of 0.42 T at 77 K, 0.3 mm above the top surface. The improved trapped field values are explained on the basis of improvements in the microstructure.

Effect of vibration frequency on primary phase and properties of grey cast iron fabricated by lost foam casting

The properties of gray cast iron (GCI) are affected by density of matrix, size of flake graphite and primary austenite. In this paper, the Y-type specimen of GCI was prepared by lost foam casting (LFC) with and without vibration, and the influence of vibration frequency on the density of matrix, size of primary phase, and properties of the GCI was studied. The results show that the length of the flake graphite and the size of the primary austenite in GCI firstly decrease and then increase with the increase of the vibration frequency. With a vibration frequency of 35 Hz, the length of the flake graphite is the shortest, the primary austenite is the finest and the density of the matrix is the highest. In addition, the tensile strength, elongation and hardness of the GCI firstly increase and then decrease with the increase of the vibration frequency, due to the refinement of the primary phase and the increase of the matrix density. In order to analyze the refinement mechanism of the primary phase of the GCI fabricated by the LFC with vibration, the solidification temperature fields of the GCI fabricated by the LFC with the vibration frequency of 0 and 35 Hz were measured. The results show that the vibration reduces the eutectic point of the GCI and increases the supercooling degree during the eutectic transformation. As a result, the length of the flake graphite and the size of the primary austenite in GCI fabricated by LFC with the vibration frequency of 35 Hz decrease.

Characterization of cast manganese steels containing varying manganese and chromium additions

Three manganese steel containing 13–17 wt.% manganese and varying amounts of chromium were produced by casting technique. The microstructures of the cast manganese steels were observed using optical microscopy (OM) techniques. The hardness properties of the steels were evaluated using the Vickers microhardness testing. Although secondary precipitates were identified at the grain boundaries of the cast steels, the results showed that varying addition of manganese and chromium has significant effects on improving the microstructure of the steels. Improvement in the microhardness properties resulted from both the secondary phase and grain refinement properties of the alloying elements. The wear behaviour shows that addition of different weight percent of the chromium content decreases the coefficient of friction of the manganese steels. The corrosion behaviour results gotten from 3.5% NaCl solution showed that Mn and Cr additions influenced the corrosion property of the material.

Joint Amplitude and Phase Refinement for Monaural Source Separation

Monaural source separation is often conducted by manipulating the amplitude spectrogram of a mixture (e.g., via time-frequency masking and spectral subtraction). The obtained amplitudes are converted back to the time domain by using the phase of the mixture or by applying phase reconstruction. Although phase reconstruction performs well for the true amplitudes, its performance is degraded when the amplitudes contain error. To deal with this problem, we propose an optimization-based method to refine both amplitudes and phases based on the given amplitudes. It aims to find time-domain signals whose amplitude spectrograms are close to the given ones in terms of the generalized alpha-beta divergences. To solve the optimization problem, the alternating direction method of multipliers (ADMM) is utilized. We confirmed the effectiveness of the proposed method through speech-nonspeech separation in various conditions.

Influence of continuous laser treatment on microstructural evolution and mechanical properties of forged Ti-Zr alloy

The influence of different continuous laser injection parameters on microstructure, phase evolution and mechanical properties of Ti-30Zr-5Al-3V (30Zr, wt%) is systematically investigated. The as-prepared 30Zr alloy consists of α and β phase, whereas the surface of 30Zr alloy is composed of α′, α and β phases after laser surface re-melting (LSR). The surface microstructure of laser-treated 30Zr alloys is significantly refined and nanocrystalline is observed in the outermost layer after LSR. The top surface hardness of laser-treated 30Zr alloys is mainly affected by the form of α′ phase and microstructural refinement. Herein, the higher laser power density and longer laser dwelling time resulted in a higher surface hardness of 30Zr alloy. The cross-sectional microhardness of laser-treated 30Zr alloys decreased with increasing distance from the alloy surface.

Mechanism of phase refinement and its effect on mechanical properties of a severely deformed dual-phase Mg–Li alloy during annealing

Microstructure evolution of severely cold rolled dual-phase Mg–Li alloy during annealing at various temperatures was systemically investigated. The results showed that severely deformed α-Mg phase can be significantly refined by annealing process. α-Mg phases were first stratified into various layers by phase transformation from α-Mg phase into β-Li phase. Low angle grain boundary was more easily inducing phase transformation compared to high angle one during annealing. α layers continuously broken into chains of α grains at high annealing temperature, which is controlled by the motion of triple junction at the intersection of phase and grain boundary. Grain boundaries exhibited a high interface tension compared to phase boundary, which drove the globularization of α-Mg grains. Mechanical properties and strain hardening behavior were influenced by phase refinement. Coordination of grain refinement and phase refinement promoted the ductility of dual-phase Mg–Li alloy without a remarkable decrease in strength.

Microstructural evolution and mechanical properties of ternary Al–Fe–Nb alloy under free fall condition

Ternary Al55Fe40Nb5 alloy was rapidly solidified in 3 m drop tube to investigate its solidification evolution and mechanical properties at high cooling rates and undercoolings. The microstructure of this alloy was composed of the primary FeAl dendrite, the (FeAl + Nb(Fe, Al)2) eutectic and the composite of FeAl, FeAl2 and Nb(Fe, Al)2 phases. As the alloy droplet diameter varied from 1200 to 80 μm, the growth morphology of primary FeAl phase evolved from coarse dendrite to refined dendrite, and finally into equiaxed grain. Meanwhile, the eutectic and the composite exhibited a regular to anomalous microstructure transition, and the Nb(Fe, Al)2 phase changed from aggregation growth to uniform distribution. Consequently, the homogenous reticulate-shaped particulate structure formed. The microscopic structures of the three intermetallic compound phases were explored by HRTEM technique. Under the influences of large undercooling and cooling rate, the grain refinement of primary phase and the homogenous distribution of three phases led to the increase of Vickers microhardness for this rapidly solidified alloy.

Achieving outstanding combination of strength and ductility of the Al-Mg-Li alloy by cold rolling combined with electropulsing assisted treatment

Outstanding combination of strength and ductility of the Al-Mg-Li alloy could be achieved using the efficient and energy saving route of cold rolling combined with two steps of electropulsing assisted treatment (EAT), namely, the electropulsing assisted recrystallization annealing (EARA) and electropulsing assisted ageing (EAA). It was found that the EARA tremendously promoted the recrystallization behavior of the cold rolled alloy, leading to the grain refinement and texture weakening. Besides, the following EAA accelerated the coarsening of the strengthening δ′ phase. As a result, there was a remarkable improvement in strength and ductility, among which the increase in strength was mainly due to the combined effect of precipitation of δ′ phase and grain refinement, while the increase in elongation was mainly attributed to the grain refinement and texture modification. The rapid recrystallization during EARA was substantially attributed to the promotion effect of electropulsing on dislocation climb, which further resulted from not only the higher diffusion coefficient of vacancies under the application of electropulsing but also the another diffusion flux of vacancies induced by electro-migration.

Mechanical property study on C90300 copper composites reinforced with rare earth oxide

The copper alloys with conventional grain structure and size are soft materials with relatively low yield strength. The strength of copper based CMCs increases with the reinforcement addition. In the present experiment we have gone with Tin bronze as the matrix, an alloy of copper since it has got superior properties compared to copper due to the incorporation of Tin. The experiment revolves around the development of composite of Tin bronze with Rare Earth Oxide addition. Addition of Rare Earth Metal results in grain refinement and thus helps in increasing the mechanical properties of the material. The Tin Bronze C90300 with 1%, 2%, 3%, 4% and 5% cerium oxide weight percentage were cast. The composites were characterized by X-ray diffraction, Optical microscopy and Scanning Electron Microscopy. The composites were also sent for chemical analysis to adjudge its chemical composition. The effect of rare earth oxide addition on the mechanical properties were investigated by Rockwell hardness test and tensile test. The results showed that addition of cerium resulted in the microstructure refinement and formation of intermetallic phases, which causes pinning effect at the boundaries and increases the hardness and tensile strength of the cast sample.

Microstructure evolution of a high-strength low-alloy Zn–Mn–Ca alloy through casting, hot extrusion and warm caliber rolling

Through casting, hot extrusion and then warm caliber rolling, biodegradable Zn-0.8Mn-0.4Ca alloy exhibits yield strength (YS) of 245 MPa, ultimate tensile strength (UTS) of 323 MPa, and elongation to failure (EL) of 12%. Its strengths are better than most of the existing biodegradable Zn alloys with ELs of 10–15%. So the alloy can be considered as a more competitive candidate for making bone screws or intravascular stents. Ca has a high efficiency of forming CaZn13 phase, the equilibrium volume fraction of which reaches 10.23 vol% with the minor addition of 0.43 wt% Ca. The CaZn13 particles not only impede dislocation motion, but also stimulate recrystallization of Zn grains, resulting in a considerable strengthening effect. The average size of Zn dendrites in the as-cast alloy reaches 289 μm, while that of Zn grains in the as-rolled alloy is 5.0 μm. On the other hand, the minor Ca addition severely decreases the ductility of the Zn-0.8Mn base alloy due to the large size of CaZn13 particles inherited from the as-cast microstructure. Although their average size is reduced to 12.9 μm after the caliber rolling, it is about five times of that of MnZn13 particles. For design and fabrication of Ca-containing Zn alloys in future, refinement of CaZn13 phase should be a matter of vital concern.

Enhancement of cyclic oxidation resistance and effect of transition oxides on wear mechanism of yttrium plus aluminium modified tribaloy T-900 alloy

This paper investigated the microstructure, cyclic oxidation behaviour and wear mechanism of modified and unmodified Tribaloy T-900. Yttrium and aluminium addition promoted the selective oxidation of Al, which reduced the oxidation rate by forming continuous protective layer of Al2O3 at 1000 °C. Al2O3 layer hindered the formation of simultaneous internal oxidation and nitridation zone. Yttrium addition transforms the mechanism of grooving wear to rolling wear by increasing the surface passivation and adherence of transition oxides scale during sliding wear. Hardness of T-900Al and T-900AlY was increased due to refinement of Laves phase and precipitation of grey intermetallic phase.

Improvement of corrosion penetration resistance for aluminum heat exchanger by alloying zirconium

Corrosion of the aluminum multi-port extrusion (MPE) leads to heat exchanger leakage. Corrosion of the 1xxx series aluminum MPE tubes proceeds continuously along Al13Fe4, which is the precipitation phase of Fe impurity. The continuous corrosion behavior along Al13Fe4 rapidly propagates into the aluminum MPE tube, thereby reducing the penetration life. In this study, Zr was added in order to control the dispersion of Al13Fe4 precipitates in an attempt to improve the corrosion resistance of A1070 aluminum MPE tubes for heat exchangers. The refinement and dispersion of Al13Fe4 phase was controlled by the addition of Zr, which is a highly insoluble element in aluminum. Zr plays a role in increasing nucleation and inhibiting the growth of the surrounding Al13Fe4 phase during the precipitation to Al3Zr phase. As a result, the size of the Al13Fe4 phase became finer and more dispersed, and the continuous corrosion tendency was decreased. Therefore, corrosion propagation of aluminum MPE tube progressed uniformly and penetration was suppressed.