Phase Transformation Properties Research Articles

Influence of Thermal Modification on Al-Si Coating of Hot-Stamped 22MnB5 Steel: Microstructure, Phase Transformation, and Mechanical Properties

The hot-stamped steel with ultrahigh strength is a promising material for the fabrication of automotive components. However, the coating on the sheet surface leads to a softening problem in the welded joint. Instead of the costly coating removal process, heat treatment is an economical and effective method for the diffusion process, which can decrease the Al concentration in the coating. In this study, a preheating treatment was carried out on Al-Si-coated 22MnB5 hot-stamped steels for the homogeneity of Al, followed by laser welding and hot stamping. The effects of the preheating on the microstructure and mechanical properties of the laser-welded joints were investigated. With the preheating treatment, the Al-Si coating transformed into an Fe-Al intermetallic compound and the difference in Al content between the coating and substrate was reduced. The Al content in the weld of the specimen with the preheating treatment was reduced, compared with that without the preheating treatment. The amount of δ-ferrite in the weld after laser welding was reduced largely. The distribution of long-bland-like segregation was changed to a fine and uniform distribution. With the preheating treatment, the tensile strength of the welded joint was significantly improved and comparable to that of the decoated joint. In conclusion, the preheating treatment before the welding is an effective method to suppress the formation of δ-ferrite and improve the mechanical properties of the welded joint.

Phase transformation and dielectric properties of Y doped HfO2 thin films

In this work, we investigated the dielectric properties of yttrium (Y) doped hafnium oxide (HfO2) films using metal-insulator-semiconductor structures with various Y contents and film thicknesses. A phase diagram was built to explain the variations in the crystal structure and dielectric properties for Y doped HfO2 based films as a function of Y content and film thickness. This phase diagram would be a useful tool for optimising the electrical properties of Y doped HfO2 based thin films.

Heat capacity of samarium titanates and phase equilibria of Sm2O3-TiO2 system

Sm2TiO5 and Sm2Ti2O7 rare earth are synthesized by solid state reaction in air at temperature 1673 K using Sm2O3 and TiO2 oxides as starting materials. Their high temperature heat capacities and phase transformation properties are determined by differential scanning calorimetry and ultra-high temperature differential thermal analysis, respectively. This work detects the structure transformation between orthorhombic and hexagonal Sm2TiO5 and confirms the existence of Sm4Ti3O12 above 1945 K by quenching the laser melted samples. CALPHAD assessment of Sm2O3–TiO2 system is performed based on new and published experimental data.

Analysis of Phase Transformation and Mechanical Properties of 55CrMo Steel during Induction Hardening

Abstract To optimize the parameters of induction hardening and improve the surface hardness distribution of ball screw, the effects of the induction heating temperature on the microstructure and mechanical properties of 55CrMo steel were investigated. The specimens were heated up to 800°C, 850°C, 900°C, 950°C, 1,000°C, or 1,100°C by the induction heating power supply. Microstructural characterization of specimens was performed using an optical microscope and a high-resolution scanning electron microscope. The volume fraction of the retained austenite was measured using an X-ray diffractometer. The mechanical properties were evaluated by a microhardness tester and an electronic universal testing machine. The results show that the volume fraction of martensite in the hardened specimen increases with the increasing of heating temperature. A mixed microstructure consisting of ferrite + pearlite, bainite, and martensite is produced because of the nonfully and nonuniform austenitic state of original microstructure as the heating temperature is at 800°C. A full martensite can be produced as the heating temperature is more than 850°C. The volume fraction of retained austenite in the hardened specimen is lower when the heating temperature is in the range of 850°C–950°C; nonetheless, the volume fraction of retained austenite increases, and the tensile strength of the specimen reduces with the increasing of the heating temperature when the heating temperature is more than 950°C. The 55CrMo steel has good microstructure and mechanical properties and can meet the requirements of ball screw when the induction heating temperature is in the range of 850°C–950°C.

Prepration and Properties of Blue Tungsten Oxide Nanopowders by High Energy Ball-Mill

The purpose of this study is to prepare WO3 nanopowders by high-energy milling in mixture gas (7 % H2+Ar) with various milling times (10, 30, and 60 min). The phase transformation, particle size and light absorption properties of WO3 nanopowders during reduction via high-energy milling are studied. It is found that the particle size of the WO3 decreases from about 30 μm to 20 nm, and the grain size of WO3 decreases rapidly with increasing milling time. Furthermore, the surface of the particles due to the pulverization process is observed to change to an amorphous structure. UV/Vis spectrophotometry shows that WO3 powder with increasing milling times (10, 30, 60 min) effectively extends the light absorption properties to the visible region. WO3 powder changes from yellow to gray and can be seen as a phenomenon in which the progress of the color changes to blue. The characterization of WO3 is performed by high resolution X-ray diffractometry, Field emission scanning electron microscopy, Transmission electron microscopy, UV/Vis spectrophotometry and Particle size analysis.

The Mechanism of Thermal Transformation Hysteresis in Zro 2-Ceo 2 Shape-Memory Ceramics

Hysteresis is an important phase transformation property to understand and control in shape-memory materials. While a detailed understanding of hysteresis has been developed in shape-memory alloys (SMAs), it is far less understood in emerging shape-memory ceramics (SMCs). Here, we systematically study thermal hysteresis of the tetragonal-monoclinic martensitic transformation in ZrO2-CeO2 SMCs. We present calorimetry measurements of thermal hysteresis, which reveal a non-monotonic trend with CeO2 content as well as significant rate dependence, and correlate these findings with the transformation crystallography measured by in situ X-ray diffraction. We quantitatively analyze these results in the framework of martensite nucleation theory and conclude that the initial decrease in hysteresis with CeO2 content can be attributed to improving interface compatibility (λ2) for coherent nucleation whereas the sharp increase in hysteresis at higher CeO2 contents (below temperatures of ~773 K) is a result of interface friction consistent with thermally-activated interactions with the Peierls barrier of the crystal. Our analysis gives an activation energy of ~136 kJ/mol, which is consistent with previously reported activation energies of isothermal transformation in these materials. These findings clarify contradicting reports in the ZrO2 literature and confirm that the same controlling factors of hysteresis in SMAs, namely λ2 and thermal friction, are also operative in SMCs.

Influence of low Bi contents on phase transformation properties of VO2 studied in a VO2:Bi thin film library.

A thin-film materials library in the system V–Bi–O was fabricated by reactive co-sputtering. The composition of Bi relative to V was determined by Rutherford backscattering spectroscopy, ranging from 0.06 to 0.84 at% along the library. The VO2 phase M1 was detected by X-ray diffraction over the whole library, however a second phase was observed in the microstructure of films with Bi contents > 0.29 at%. The second phase was determined by electron diffraction to be BiVO4, which suggests that the solubility limit of Bi in VO2 is only ∼0.29 at%. For Bi contents from 0.08 to 0.29 at%, the phase transformation temperatures of VO2:Bi increase from 74.7 to 76.4 °C by 8 K per at% Bi. With X-ray photoemission spectroscopy, the oxidation state of Bi was determined to be 3+. The V5+/V4+ ratio increases with increasing Bi content from 0.10 to 0.84 at%. The similarly increasing tendency of the V5+/V4+ ratio and Tc with Bi content suggests that although the ionic radius of Bi3+ is much larger than that of V4+, the charge doping effect and the resulting V5+ are more prominent in regulating the phase transformation behavior of Bi-doped VO2.

Characterization of Debris Formed in Magnetic Field-Assisted EDM Using Two-Phase Dielectric Fluid

The present research was focussed to investigate the influence of liquid-gaseous dielectric on debris formation in magnetic field-assisted electrical discharge machining. The air and argon gas were used to make two-phase dielectric fluids such as liquid-air and liquid-argon gas, respectively. Experimentation was conducted to compare the effect of different liquid-gaseous dielectric environments on debris formation. The morphology and diameter distribution of debris were analyzed. In addition, the effect on elemental analysis, phase transformation and magnetic property of debris was investigated. The experimental results showed the exothermic reaction due to air from liquid–air dielectric, and inert property of argon gas from liquid-gaseous dielectric affected the formation of debris. The XRD results confirmed the formation of oxides in the debris produced using liquid-air mixed dielectric. The oxide-free debris formed while using the argon gas. Low saturation of magnetization was found in the debris, formed in the liquid–air dielectric which showed the weak attraction toward magnet when compared with that in the liquid–argon gas mixed dielectric.

Laser power modulated microstructure evolution, phase transformation and mechanical properties in NiTi fabricated by laser powder bed fusion

In this study, two sets of optimized laser powder bed fusion (LPBF) additive manufacturing parameters with similar energy density but different laser powers (HP: high laser power with high scanning speed, LP: low laser power with low scanning speed) were used to produce fully dense and crack-free NiTi samples. The microstructure, phase transformation and mechanical properties of the LPBF fabricated HP and LP NiTi were investigated using scanning electron microscopy (SEM), differential scanning calorimeter (DSC), X-ray diffraction (XRD) and dynamic mechanical analysis (DMA). The results showed that the HP and LP NiTi samples had different microstructures, phase transformation temperatures and mechanical properties. It was found that the HP NiTi samples predominantly contained austenite at room temperature and exhibited lower phase transformation temperatures. In contrast, the LP NiTi samples contained a large amount of martensite and had larger thermal memory recovery and better damping capacity. Additionally, the microstructure, phase transformation temperatures and mechanical properties were found to vary at different locations along the building direction in both HP and LP NiTi. This study implies that by manipulating the LPBF processing parameters, in particular the laser power, the phase transformation, microstructure and dynamic mechanical properties of the LPBF fabricated NiTi can be controlled to target different applications.

Ultrasonic vibration-assisted laser directed energy deposition in-situ synthesis of NiTi alloys: Effects on microstructure and mechanical properties

Abstract Nickel-Titanium (NiTi) alloys have the unique shape memory effect and pseudoelasticity, good damping capacity, good corrosion resistance, and excellent biomechanical compatibility. These properties make NiTi alloys attractive in industries like automobile, aerospace, medical device, etc. However, it’s difficult to fabricate and machine NiTi alloys due to their rapid work-hardening property and pseudoelasticity. Traditional manufacturing methods, such as casting and powder metallurgy, show disadvantages of high cost, time-consuming, and limitations in fabrication of parts with complex geometry. In order to reduce or solve these problems, laser additive manufacturing (LAM) methods have been applied for the fabrication of NiTi alloys. Among the LAM methods, laser directed energy deposition (DED) in-situ synthesis of NiTi alloys from the premixed Ni and Ti powders shows its unique advantages of cost-effectiveness and flexibility in altering NiTi alloys’ phase transformation and mechanical properties. However, heterogeneous microstructures and the formation of secondary phases are two crucial issues that impede the application of laser DED to in-situ synthesis NiTi alloys. Ultrasonic vibration has pronounced effects on liquid materials solidification processes, which could be utilized in homogenizing the microstructure and reducing the secondary phase of laser DED in-situ synthesized NiTi alloys. This paper, for the first time, reports in-situ synthesis of NiTi alloys by laser DED with ultrasonic vibration assistance. The effects of ultrasonic vibration on microstructure properties (microstructure homogeneity, internal defects, elemental composition, grain size, and phase constituents) and mechanical properties (pseudoelasticity, microhardness, and Young’s modulus) have been investigated.

Effects of Ru content on phase transformation and compression property of cast TiAl alloys

Ruthenium (Ru) is a promising element to heighten the comprehensive mechanical properties of TiAl alloys. In the present study, the phase transformation during the cooling of Ti-47Al-2Cr-2Nb-xRu (x=0, 0.1, 0.5, 1.0, at.%) alloys was investigated. The results show that Ru tends to segregate in the interdendritic region during solidification, and therefore, refines the as-cast microstructure of the alloys. As a β-stabilizer, Ru does not induce a novel solidification reaction but maintains the peritectic reaction of L+β→α. An excessive Ru content would cause the formation of (γ+τ1+B2) and (α+γ+τ1+B2) phase regions below 1,250 °C. The precipitation of τ1-containing mixture is attributed to the Ru-segregation, which inhibits the reaction of α→γ and facilitates the formation of B2 phase. The discontinuous coarsening of γ phase and block τ1 phase formed alternately in a manner of analogous eutectoid decomposition within B2 phase. In addition, the effect of Ru content on compression property of the alloys was studied. The yield strength increases up to 427 MPa at 800 °C with the addition of 1.0at.% Ru, which is mainly due to the solution strengthening effect of Ru.

Phase transformation and magnetic properties of fully dense Sm(Fe0.8Co0.2)11Ti bulk magnets

High density sintered Sm(Fe0.8Co0.2)11Ti bulk magnets were successfully produced using a newly developed high pressure pressing fabrication method. The purity of the hard magnetic ThMn12 phase in the bulk magnet reached to higher than 97 wt.%. The phase transformation behavior from amorphous to ThMn12 phase during heat treatment was systematically investigated by transmission electron microscopy. The remanent magnetization and maximum energy product of a bulk magnet were 96.0 emu/g and 12.22 MGOe, respectively. To the best of our knowledge, the achieved maximum energy product is the highest among all the SmFe12-based bulk magnets reported.

Spark plasma sintering of a lunar regolith simulant: effects of parameters on microstructure evolution, phase transformation, and mechanical properties

The spark plasma sintering (SPS) process is a potentially effective in-situ resource utilization (ISRU) technology for consolidating lunar regolith in order to produce structural components for future space exploration. This study examined the fundamental mechanisms of the effects of SPS conditions on microstructure evolution, phase transformation, and mechanical properties. For this purpose, a lunar regolith simulant (FJS-1) was selected and sintered for a total of 16 cases based on four primary SPS testing parameters: temperature, applied external pressure, dwell time, and heating rate. The Taguchi design method was used to examine the effects and sensitivity of each testing parameter. Laboratory tests were conducted in multiple length scales, including density, porosity, optical microscopy, scanning electron microscopy aided by energy-dispersive spectroscopy, transmission electron microscopy, nanoindentation, and strength testing (in both compressive and flexural). Taguchi analysis results of SPS parameters and sintering mechanism discussion indicated that the sintering temperature is the dominant factor changing microstructure heterogeneity and densification during the SPS process. The contribution of applied pressure to the surface and the grain boundary diffusion rate and the nucleation rate indicated that the applied pressure may have enhanced both phase transformation and homogeneity during the sintering process. Strength of the sintered samples were approximately 10 times greater than those of a typical plain concrete. The collective results indicate that the SPS technology, a potentially viable ISRU method, can be used to produce property-specific and application-targeted building components on the lunar surface.

Effect of Si element on phase transformation and mechanical properties for FeCoCrNiSix high entropy alloys

In present research, the phase evolution and mechanical properties of FeCoCrNiSix high-entropy alloys were investigated by using different testing techniques. The results showed that Si element can promote the formation of BCC phase and had a significant effect on the micro-hardness and wear resistance of alloys. The micro-hardness of HEAs increased from 89.52 HV to 653.71 HV and the depth of the wear track decreased from 22.139 μm to 5.292 μm with the addition of Si element. When x was equal to 1 (FeCoCrNiSix), the alloy possessed the highest micro-hardness and best wear resistance. Moreover, the wear mechanism was transformed into abrasive wear according to the wear tracks measurements due to the addition of Si elements.

Steel sheets partnered with quenchable sheet in hot stamping of tailor-welded blanks and its application to separation prevention of fractured components

The phase transformation and mechanical properties of non-quenchable steels partnered with the quenchable boron steel in hot stamping of tailor-welded blanks were evaluated to produce tailored components with partially balanced strength and ductility. The effect of the forming start temperature after natural air cooling on the phase transformation and mechanical properties for 270 MPa mild steel, non-quenchable steel, 440 MPa high strength steel, and 22MnB5 steel sheets was examined, and the 270 MPa and non-quenchable sheets had enough ductility after hot stamping. Tailored components having a hardness of about 500 HV1 in the high strength zone and a total elongation of about 30% in the high ductility zone were hot-stamped from a tailor-welded blank composed of 22MnB5 and 270 MPa sheets. It was found that the 270 MPa mild steel sheet is sufficient as a partner sheet of tailor-welded blanks. In addition, the safety of hot-stamped components was heightened by welding a 22MnB5 main blank with a 270 MPa steel patch. Even if the main blank is fractured by a collision, the hot-stamped component is not separated by the 270 MPa patch having high ductility.

Microstructure and mechanical properties of Al-Mg-Li-Sc-Zr alloy processed by spray deposition and thermo-mechanical processes

Al-Mg-Li-Sc-Zr alloy was prepared by spray deposition followed by extrusion and heat treatment processes. The effects of aging temperature on microstructure, phase transformation, and mechanical properties of the alloy were studied. The results show that the extruded alloy presents a typical fibrous structure with large amounts of secondary phases distributed along the extrusion direction. After solution and aging treatments, recrystallized structures are founded in the alloy, and the proportion of large size grains increases with the aging temperature increasing. TEM observation shows that the δ′(Al3Li) phase particles are homogeneously distributed in the Al matrix, leading to a significant enhancement of tensile strength. The yield strength (YS), ultimate tensile strength (UTS), and elongation (EL) of the alloy after aging at 120 °C for 20 h reach 492.3 ± 9 MPa, 568.2 ± 6 MPa, and 5.8% ± 0.25, respectively. When the aging temperature rises from 120 to 160 °C，the dispersed δ′phases are coarsened gradually and the continuous striped S1(Al2MgLi) phases are observed at the grain boundaries, which causes the declination of strength and elongation of the alloy.

Effects of rapid heating and uniaxial loading on the phase transformation and mechanical properties of direct partial remelted butt joint of AISI D2 tool steel

Tool steels are widely used in various industries, such as automotive, shipbuilding, manufacturing, and marine, for rolling mills, blanking metals, and punching dies, given their distinctive hardness, resistance to abrasion, and deformation. However, joining tool steels using the conventional fusion welding process is difficult because of the formation of dendritic structures and hot cracking, which affect the strength of joining. Therefore, this study proposed the direct partial remelting process (DPRMP) for the butt joining of AISI D2 tool steel. Moreover, different uniaxial loads of 0, 0.5, 2.5, and 5 N were applied during the joining process to investigate the microstructural evolution and mechanical properties of DPRMP samples. Results showed that the ferrite phase in the base material was changed to the austenite phase with globular shape in the joined samples through DPRMP. In addition, increasing the uniaxial load from 0 N to 5 N reduced the average grain size, increased the shape factor, and caused joining defects, such as voids, to disappear. Furthermore, the tensile strength of the DPRMP samples improved by increasing uniaxial loading from 0 N to 5 N due to the effect of grain boundary diffusion and the decrease in eutectic carbide at the joint interface. The highest tensile strength was achieved in DPRMP-5, with a value of 652 MPa and a welding efficiency of 103%. Moreover, the average hardness value of the fusion zone improved in the DPRMP samples and increased to 400 HV wherein the as-received material presented a value of 226 HV.

Cuboid-like nanostructure strengthened equiatomic Ti–Zr–Nb–Ta medium entropy alloy

This study investigates the effect of annealing treatment on the phase transformation and mechanical properties of the equiatomic TiZrNbTa MEA from room temperature to 1200 °C. After annealing at 1200 °C for 24h, the single solid-solution body-centred cubic (BCC) phase in the as-cast Ta25Zr25Nb25Ti25 transformed into an extremely high number density (~103/μm2) of Ta–Nb-rich BCC nanocuboidal phase (28 ± 10 nm square, BCC1) and a nanostrip-like Zr-rich BCC phase (3 ± 2 nm thick, BCC2). The phase separation from BCC to BCC1 and BCC2 arises from two primary reasons: (i) the high positive mixing enthalpy of both Ta–Zr and Nb–Zr (strong tendency to separation between each pair), and (ii) the 3–4 orders of magnitude higher mobility of Zr than Ta, Nb and Ti in these MEAs (kinetically driven). Detailed CALPHAD simulations of phase formation in this MEA agreed with experiments and provided insightful phase transformation details. The calculated diffusion distance of Zr (~4.1 nm) from the CALPHAD data corresponds to the measured Zr-rich nanostrip thickness (3 ± 2 nm). The nanocuboidal BCC1-BCC2 structure exhibited 112<111>-type of twinning deformation under compression at room temperature. The Ta25Zr25Nb25Ti25 MEA retained yield strength of ~410 MPa at 1000 °C and ~210 MPa at 1200 °C. The phase transformation during cooling after annealing and the microstructural evolution during compression at temperatures from 600 °C to 1200 °C were characterized and discussed in detail.

Effect of ZnO on the phase transformation and optical properties of silicate glass frits using rice husk ash as a SiO2 source

This research attempts to propose the fabrication and characterization of highly amorphous zinc silicate glasses derived from zinc oxide (ZnO) and white rice husk ash (WRHA). Three zinc silicate glasses were produced based on empirical formula (ZnO)x(WRHA)1−x where x=0.50, 0.55 and 0.60wt.% by using melt-quenching methods. When ZnO increased, the transparency of the three glasses increased. Meanwhile, X-ray diffraction (XRD) analysis of the zinc silicate glasses revealed that the glassy state of the zinc silicate glasses increased along with the increment of ZnO, and at lowest ZnO (0.50wt.%), the presence of silicon dioxide (SiO2) peak were observed showing uncomplete melted of silica. Additional vibrational band due to the presence of tridymite was found in the Fourier transform infrared spectroscopy (FTIR) at lowest ZnO content supporting the XRD result while other glasses showed the formation of zinc silicate glasses with the presence of SiO4 and ZiO4 vibrational band. The zinc silicate absorption also increased as the ZnO increased as a result from the formation of non-bridging oxygen (NBO's). Hence, optical band gap of zinc silicate glasses was decreased from 4.35 to 4.23eV as the ZnO increased due to increment of NBO's. All zinc silicate glasses showed three different emission peaks which is at 535, 596 and 728nm correspond to green, yellow and red emission respectively. This luminescence properties of zinc silicate were attributed to the defect inside the ZnO particle.

Phase transformation and magnetocaloric effect of Co-doped Mn–Ni–In melt-spun ribbons

Ribbon-shaped magnetocaloric materials are favorable to achieve high heat-transfer efficiencies due to their large specific surface area. In this work, Mn50Ni41−xIn9Cox (0 ≤ x ≤ 4) ribbons were prepared using a melt-spinning technique, and the corresponding phase transformation and magnetocaloric properties were studied. The large temperature gradient during melt-spinning caused the initial austenite in the ribbons to form typical columnar-shaped grains with a strong ⟨001⟩A preferred orientation perpendicular to the ribbon plane. After cooling, the ribbons undergo martensitic transformation from cubic austenite to monoclinic eight-layered modulated (8 M) martensite. High angle annular dark field-scanning transmission electron microscopy observations indicate that martensite lattice modulation is inhomogeneous at atomic scales. Co substitution for Ni not only strongly influences the phase transformation temperatures but also greatly enhances ferromagnetic coupling. As a result, an enlarged magnetization difference across the martensitic transformation under a field change of 5 T in the Mn50Ni38In9Co3 ribbon induces a large magnetic entropy change up to 12.1 J kg−1 K–1 and a refrigeration capacity of 197 J kg–1 around room temperature. In addition, a wide operational temperature region up to 31 K is obtained in the Mn50Ni37In9Co4 ribbon due to the enhanced sensitivity of the transformation temperature shift under a magnetic field.