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High heat input welding can improve welding efficiency, but the impact toughness of the heat-affected zone (HAZ) deteriorates significantly. Thermal evolution in HAZ during welding is the key factor affecting welded joints’ microstructures and mechanical properties. In this study, the Leblond–Devaux equation for predicting phase evolution during the welding of marine steels was parameterized. In experiments, E36 and E36Nb samples were cooled down at different rates from 0.5 to 75 °C/s; the obtained thermal and phase evolution data were used to construct continuous cooling transformation diagrams, which were used to derive the temperature-dependent parameters in the Leblond–Devaux equation. The equation was then used to predict phase evolution during the welding of E36 and E36Nb; the quantitative experimental phase fractions of the coarse grain zone were compared with simulated results to verify the prediction results, which are in good agreement. When heat input is 100 kJ/cm, phases in the HAZ of E36Nb are primarily granular bainite, whereas for E36, the phases are mainly bainite with acicular ferrite. When heat input increases to 250 kJ/cm, ferrite and pearlite form in both steels. The predictions agree with experimental observations.

For investigating the influence mechanism underlying ultrafine Ti(C, N) within micron Ti(C, N)-based cermets, three cermets including diverse ultrafine Ti(C, N) contents were employed. In addition, for the prepared cermets, their sintering process, microstructure, and mechanical properties were systematically studied. According to our findings, adding ultrafine Ti(C, N) primarily affects the densification and shrinkage behavior in the solid-state sintering stage. Additionally, material-phase and microstructure evolution were investigated under the solid-state stage from 800 to 1300 °C. Adding ultrafine Ti(C, N) enhanced the diffusion and dissolution behavior of the secondary carbide (Mo2C, WC, and (Ta, Nb)C) under a lower sintering temperature of 1200 °C. Further, as sintering temperature increased, adding ultrafine Ti(C, N) enhanced heavy element transformation behaviors in the binder phase and accelerated solid-solution (Ti, Me) (C, N) phase formation. When the addition of ultrafine Ti(C, N) reached 40 wt%, the binder phase had increased its liquefying speed. Moreover, the cermet containing 40 wt% ultrafine Ti(C, N) displayed superb mechanical performances.

In this study, a pulsed laser was used as the heat source for the additive work. The Ti6Al4V/Inconel 718 alloy wire was deposited on the substrate by melting using a pulsed laser. Using the above method, single-layer and double-layer samples were printed. The sample material printed in this way is highly utilized. Compared to the complicated pre-preparation work of metal powder pre-mixing, this printing method is simple to prepare and only requires changing the wire feeding speed. The study of this paper provides a theoretical guide for the subsequent fusion deposition of heterogeneous wire materials. The samples were analyzed after molding using SEM, EDS and XRD to characterize the microstructure of the samples. The samples can be divided into three zones depending on the microstructure, the bottom columnar crystal zone, the middle mixed phase zone, and the bottom equiaxed crystal zone. From the bottom to the top of the sample, the phase microstructure changes as γ + Laves → α + β + Ti2Ni + TiNi + Ni3Ti → α + β. The hardness data show that the highest value in the transition zone is 951.4 HV. The hardness of the top part is second only to the transition zone due to a large number of equiaxed crystals. The bottom region is dominated by columnar crystals and is the softest of the three regions with the lowest hardness value of 701.4 HV.

In order to explore the microstructure evolution of an Mg-RE alloy refined by Al during solution treatment, an Mg-3Y-4Nd-2Al alloy was treated at 545 °C for different time periods. Phase evolution of the alloy was investigated. After solution treatment, the Mg-RE eutectic phase in the Mg-3Y-4Nd-2Al alloy dissolves, the granular Al2RE phase does not change, the acicular Al11RE3 phase breaks into the short rod-like Al2RE phase, and the lamellar Al2RE phase precipitates in the grains. With the extension of solution time, the precipitated phase of the lamellar Al2RE increased at first and then decreased, and its orientation relationship with the matrix is <112>Al2RE//<21¯1¯0>Mg and {111}Al2RE//{0002}Mg. The undissolved granular Al2RE phase can improve the thermal stability of the alloy grain by pinning the grain boundary, and the grain size did not change after solution treatment. Solution treatment significantly improved the plasticity of the alloy. After 48 h of solution treatment, the elongation increased to 17.5% from 8.5% in the as-cast state.

The assessment of the extent of carbonation and related phase changes is important for the evaluation of the durability aspects of concrete. The phase assemblage of Portland cements with different clinker compositions is evaluated using thermodynamic calculations. Four different compositions of cements, as specified by ASTM cements types I to IV, are considered in this study. Calcite, zeolites, and gypsum were identified as carbonation products. CO2 content required for full carbonation had a direct relationship with the initial volume of phases. The CO2 required for portlandite determined the initiation of carbonation of C-S-H. A continual decrease in the pH of pore solution and a decrease in Ca/Si is observed with the carbonation of C-S-H. Type II cement exhibited rapid carbonation at relatively less CO2for full carbonation, while type III required more CO2 to carbonate to the same level as other types of cement. The modeling of carbonation of different Portland cements provided insights into the quantity of CO2 required to destabilize different hydrated products into respective carbonated phases.

The performance of alkali-activated slag (AAS) under thermal treatment has received particular attention. In this study, the effect of five elevated temperatures (25, 200, 400, 600, and 800 °C) and two cooling methods (air cooling and water spraying) on the mechanical and durability properties, microstructure, and phase evolution of AAS was investigated. The results show that AAS mortars exhibit higher resistance to thermal attack than OPC in terms of strength and durability. AAS samples cooled in air show higher residual strength than those cooled by spraying water, which is mainly attributed to fewer cracks formed in the former. The resistance to carbonization of exposed AAS mortars depends on the pore size distribution, while that to chloride ion penetration depends on the porosity. Cooling methods show a minor effect on the phase evolution of reaction products, suggesting that the microstructure degradation is mainly responsible for the damage of AAS structures. This study provides fundamental knowledge for the thermally induced changes on AAS which contributes new ideas for the development of construction structures with higher fire resistance.

The present study investigated the structural evolution of Portland cement (PC) incorporating supplementary cementitious materials (SCMs) exposed to seawater. The samples were made with replacing Portland cement with 10 mass-% silica fume, metakaolin or glass powder. The reaction degree of SCMs estimated by the portlandite consumption shows that metakaolin has the highest reaction degree, thus metakaolin-blended PC exhibits the highest strength. The control exposed to seawater exhibited 14.82% and 12.14% higher compressive strengths compared to those cured in tap water at 7 and 28 days. The samples incorporating metakaolin showed the highest compressive strength of 76.60 MPa at 90 days tap water curing and this was 17% higher than that of the control. Exposure to seawater is found to retard the rate of hydration in all SCM-incorporating systems, while the strength development of the neat PC system is enhanced. The main reaction product that forms during exposure to seawater is Cl-AFm and brucite, while it is predicted by the thermodynamic modelling that a significant amount of M-S-H, calcite and hydrotalcite is to form at an extended period of exposure time.

CoCrFeMoNi high entropy alloys (HEAs) exhibit several promising characteristics for potential applications of high temperature coating. In this study, metastable intermetallic phases and their thermal stability of high-entropy alloy CoCrFeMo0.85Ni were investigated via thermal and microstructural analyses. Solidus and liquidus temperatures of CoCrFeMo0.85Ni were determined by differential thermal analysis as 1323 °C and 1331 °C, respectively. Phase transitions also occur at 800 °C and 1212 °C during heating. Microstructure of alloy exhibits a single-phase face-centred cubic (FCC) matrix embedded with the mixture of (Co, Cr, Fe)-rich tetragonal phase and Mo-rich rhombohedron-like phase. The morphologies of two intermetallics show matrix-based tetragonal phases bordered by Mo-rich rhombohedral precipitates around their perimeter. The experimental results presented in our paper provide key information on the microstructure and thermal stability of our alloy, which will assist in the development of similar thermal spray HEA coatings.

At present, most Mo2FeB2-based cermets are prepared by vacuum sintering. However, vacuum sintering is only suitable for ordinary cylinder and cuboid workpieces, and it is difficult to apply to large curved surface and large size workpieces. Therefore, in order to improve the flexibility of preparing Mo2FeB2 cermet, a flux cored wire with 70% filling rate, 304 stainless steel, 60 wt% Mo powder and 40 wt% FeB powder was prepared. Mo2FeB2 cermet was prepared by an arc cladding welding metallurgy method with flux cored wire. In this paper, the microstructure, phase evolution, hardness, wear resistance and corrosion resistance of Mo2FeB2 cermets prepared by the vacuum sintering (VM-Mo2FeB2) and arc cladding welding metallurgy method (WM-Mo2FeB2) were systematically studied. The results show that VM-Mo2FeB2 is composed of Mo2FeB2 and γ-CrFeNi.WM-Mo2FeB2 is composed of Mo2FeB2, NiCrFe, MoCrFe and Cr2B3. The volume fraction of hard phase in WM-Mo2FeB2 is lower than that of VM-Mo2FeB2, and its hardness and corrosion resistance are also slightly lower than that of VM-Mo2FeB2, but there are obvious pores in the microstructure of VM-Mo2FeB2, which affects its properties. The results show that WM-Mo2FeB2 has good diffusion and metallurgical bonding with the matrix and has no obvious pores. The microstructure is compact and the wear resistance is better than that of VM-Mo2FeB2.

The autogenous self-healing of cementitious material micro-cracks might lead to the service-life extension of structures. However, most of its aspects are still unknown. This paper investigates the self-healing capacity of ternary cement blends including metakaolin (MK), ground granulated blast-furnace slag (BFS), limestone (LS), and siliceous filler (F). Morphology and healing precipitation patterns were studied through the optical microscopy of artificial micro-cracks, global healing product mass monitoring, and XRD and TGA used to identify and quantify mineral formation. The self-healing potential index is introduced based on the mass measurements. It was found that the formulation containing 10% MK presented the highest healing potential at an early age (

The fabrication of transparent polycrystalline Y3Al5O12 (YAG) is still a challenge, requiring the achievement of highly pure and fully dense, homogeneous materials. An important role is played by the powder characteristics: pure, fine and unagglomerated powders are essential for achieving full density and the required microstructural features. Keeping in mind these requirements, the aim of this work was to investigate the role of different synthesis parameters during co-precipitation, which is widely used to prepare YAG powders for transparent devices. The key role of the precipitant solution is here illustrated, by comparing the effect of aqueous ammonia (AA) versus ammonium hydrogen carbonate (AHC). This latter allowed the preparation of softly agglomerated powders, characterized by a very good sinterability. However, when AHC is used, attention should be paid to its concentration. By comparing the effect of two AHC precipitant solutions (at 0.5 M and 1.5 M, respectively), only the former one allowed the preparation of pure YAG powders, free from secondary phases. In this last condition, by using both chlorides and nitrates as YAG precursors, pressureless sintering at 1500–1600 °C/3 h gave rise to pure materials, highly dense and characterized by a fine and homogeneous microstructure.

In the grinding process, the materials within the surface layer may undergo phase transformation and finally form a strengthened layer. It is of great significance to model the phase transformation and predict the characteristics of the strengthened layer accurately. The phase transformations occur under the varying temperature and high stress−strain in grinding, so the effects of stress on the transformations are inescapable. This paper focuses on revealing the effects of stress on phase transformations in grinding. For this purpose, a thermal−mechanical−metallurgical direct coupling finite element (FE) model of grinding was established in Abaqus. The coupling interactions such as the latent heat, the volume change strain caused by phase transformation, and the stress-induced phase transformation were considered in the modeling procedure. Grinding experiments were carried out and proved the model could accurately predict the microstructure distribution and thickness of the strengthened layer. Further, the evolution of the phase transformation was discussed, and the effects of stress on the transformations were revealed.

Near- α titanium alloys have extensive applications in high temperature structural components of aircrafts. To manufacture complex-shaped titanium alloy panel parts with desired microstructure and good properties, an innovative low-cost hot stamping process for titanium alloy was studied in this paper. Firstly, a series of hot tensile tests and Scanning Electron Microscope (SEM) observations were performed to investigate hot deformation characteristics and identify typical microstructural evolutions. The optimal forming temperature range is determined to be from 750 °C to 900 °C for hot stamping of TA15. In addition, a unified mechanisms-based material model for TA15 titanium alloy based on the softening mechanisms of recrystallization and damage was established, which enables to precisely predict stress-strain behaviors and potentially to be implemented into Finite Element (FE) simulations for designing the reasonable processing window of structural parts for the aerospace industry.

The microstructural evolution of Dy2O3-TiO2 powder mixtures during ball milling and post-milled annealing was investigated using XRD, SEM, TEM, and DSC. At high ball-milling rotation speeds, the mixtures were fined, homogenized, nanocrystallized, and later completely amorphized, and the transformation of Dy2O3 from the cubic to the monoclinic crystal structure was observed. The amorphous transformation resulted from monoclinic Dy2O3, not from cubic Dy2O3. However, at low ball-milling rotation speeds, the mixtures were only fined and homogenized. An intermediate phase with a similar crystal structure to that of cubic Dy2TiO5 was detected in the amorphous mixtures annealed from 800 to 1000 °C, which was a metastable phase that transformed to orthorhombic Dy2TiO5 when the annealing temperature was above 1050 °C. However, at the same annealing temperatures, pyrochlore Dy2Ti2O7 initially formed and subsequently reacted with the remaining Dy2O3 to form orthorhombic Dy2TiO5 in the homogenous mixtures. The evolutionary mechanism of powder mixtures during ball milling and subsequent annealing was analyzed.