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Additive manufacturing (AM) has gained significant attention in automotive applications, while the low weldability of AM material poses challenges when assembling AM materials with conventionally manufactured materials. This study investigated the laser welding of AM AlSi10Mg and AA1050 sheet metal in an overlap configuration, specifically focusing on the impact of placement configuration of two materials on weld properties. This aims to provide valuable insights for optimizing the localized geometry of AM components to enhance the joint performance. Results showed that positioning AM AlSi10Mg on top leads to a higher weld penetration and higher Si content within the molten pool, especially in the upper sheet. Additionally, weld zone grain structure was greatly influenced by alternating the placement configuration, where welds with AM AlSi10Mg on top exhibiting more equiaxed grains in the weld centre and refined columnar grains near the fusion boundary of upper sheet. Furthermore, significantly reduced weld porosity was determined by positioning AM AlSi10Mg at the bottom (3.2 ± 0.4 %∼7.1 ± 0.9 %) compared to placing it on top (16.9 ± 0.9 %∼20.1 ± 0.9 %) in all scenarios ranging from full penetration to partial penetration. This can be related to the fact that the hydrogen bubbles originating from AM AlSi10Mg experienced a shorter exposure in the molten pool, limiting the merging and growth of small bubbles. However, a slightly lower joint strength was determined in welds with AM AlSi10Mg at the bottom which may be due to the plastic deformation incompatibility between large columnar grains in the fusion zone and the fine grains in the as-printed material.

Coal plays a dominant role in China's energy production and consumption, which also serves as the cornerstone for energy security. The constitutive relationship of coal material is of great significance for the quantitative characterization and evaluation of mechanical properties of isolated coal pillars. From an energy perspective, coal failure is driven by energy, and the energy-based damage characterization provides a basis for the establishment of constitutive model. In this study, since the constitutive model based on the classical Lemaitre's hypothesis shows a significant error in presenting the nonlinear constitutive relationship of coal material, a correction coefficient considering the compaction effect of coal material is first introduced. Then, a novel damage constitutive model that can accurately describe the overall compression state of coal material is constructed. Finally, the theoretical model is compared with exiting models using the experimental data of five types of coal material from different mines. The results show that the evolution of energy dissipation damage variable is highly consistent with that of stress–strain relations. The established constitutive model considering energy dissipation and compaction effect can more accurately describe the nonlinear strength and deformation characteristics of coal material than the classical and existing models. Notably, this new model can be effectively extended to the single cyclic compression conditions to reproduce the loading-unloading-reloading process of coal material.

Vacuum brazing of GH3535 alloy was conducted using Au–18Ni (wt%) filler metal. The effect of brazing temperature on the microstructure and mechanical properties was investigated. Furthermore, the microstructural evolution and fracture mechanisms of brazed joints were discussed. The cross section of brazed joint could be divided into two distinctive reaction zones. The typical microstructure of the joint brazed at 1030 °C/10min was GH3535 substrate/Ni (s.s) + Mo-rich Ni (s.s) + Au-rich phase/Au (s.s) + FeNi3/Au-rich phase + Mo-rich Ni (s.s) + Ni (s.s) + GH3535 substrate. Raising the brazing temperature promoted the diffusion of elements, Ni (s.s) and Au (s.s) gradually increased, and the second phase particles consisting of FeNi3 gradually decreased. With the increase in brazing temperature, the shear strength of brazed joints first increased and then decreased. The maximum room shear strength of 420 MPa was obtained at 960 °C/25min and the high temperature shear strength of 153 MPa was obtained at 600 °C. Fracture analysis indicated that cracks initiated at the interface of Au (s.s) and then propagated along the zone of FeNi3 with dimple and tearing ridges patterns.

Nickel-based coatings were prepared by laser cladding assisted with rotating magnetic field on mild steel substrates. The effects of rotating magnetic field on the defects, microstructure, residual stress, microhardness, and wear resistance of the coatings were studied. Results revealed that the rotating magnetic field reduced pores and cracks of the nickel-based coatings. The nickel-based coatings are main composed of γ-(Ni, M), CrB, M23C6, and NbC phases. The average grain size of the coating decreased from 0.67 μm2 to 0.49 μm2 with rotating magnetic field assistance. The number of large-angle grain boundaries was increased too. At the same time, the residual stress in the coating was significantly reduced by the rotating magnetic field. Therefore, the cracking tendency of the coating was reduced. The average microhardness of the nickel-based coating increased from 422.5 HV0.2 to 515.5 HV0.2 due to fine-grain strengthening. The wear mechanisms of the coatings were mix of abrasive wear and adhesive wear. With rotating magnetic field assistance, the wear resistance of the coating was greatly enhanced. The wear rate of the coating reduced 83.7% from 85.2 μm3/(N∗m) to 13.9 μm3/(N∗m). The wear weight loss reduced 87% from 13.8 mg to 1.8 mg.

The peak dilation angle is an important mechanical feature of rock discontinuities, which is significant in assessing the mechanical behaviour of rock masses. Previous studies have shown that the efficiency and accuracy of traditional experimental methods and analytical models in determining the shear dilation angle are not completely satisfactory. Machine learning methods are popular due to their efficient prediction of outcomes for multiple influencing factors. In this paper, a novel hybrid machine learning model is proposed for predicting the peak dilation angle. The model incorporates support vector regression (SVR) techniques as the primary prediction tools, augmented with the grid search optimization algorithm to enhance prediction performance and optimize hyperparameters. The proposed model was employed on eighty-nine datasets with six input variables encompassing morphology and mechanical property parameters. Comparative analysis is conducted between the proposed model, the original SVR model, and existing analytical models. The results show that the proposed model surpasses both the original SVR model and analytical models, with a coefficient of determination (R2) of 0.917 and a mean absolute percentage error (MAPE) of 4.5%. Additionally, the study also reveals that normal stress is the most influential mechanical property parameter affecting the peak dilation angle. Consequently, the proposed model was shown to be effective in predicting the peak dilation angle of rock discontinuities.

With the continuous progress and development in biomedicine, metallic biomedical materials have attracted significant attention from researchers. Due to the low compatibility of traditional metal implant materials with the human body, it is urgent to develop new biomaterials with excellent mechanical properties and appropriate biocompatibility to solve the adverse reactions caused by long-term implantation. High entropy alloys (HEAs) are nearly equimolar alloys of five or more elements, with huge compositional design space and excellent mechanical properties. In contrast, biological high-entropy alloys (Bio-HEAs) are expected to be a new bio-alloy for biomedicine due to their excellent biocompatibility and tunable mechanical properties. This review summarizes the composition system of Bio-HEAs in recent years, introduces their biocompatibility and mechanical properties of human bone adaptation, and finally puts forward the following suggestions for the development direction of Bio-HEAs: to improve the theory and simulation studies of Bio-HEAs composition design, to quantify the influence of composition, process, post-treatment on the performance of Bio-HEAs, to focus on the loss of Bio-HEAs under actual service conditions, and it is hoped that the clinical application of the new medical alloy Bio-HEAs can be realized as soon as possible.

Background: Symptomatic vertebral artery dissecting aneurysm (VADA) is a challenging disease with controversy on treatment strategy due to anatomic configuration and their nature. Moreover, the outcomes of reconstructive treatment have not been well established. Objective: To evaluate the safety and efficacy of reconstructive endovascular treatment (EVT) for symptomatic VADAs with Willis covered stent. Methods: We evaluated retrospectively 13 patients with symptomatic VADAs who treated with Willis covered stent, compared with stent-assisted coiling (SAC) on the characteristics, posttreatment course, angiographic and clinical follow-up outcomes at an average of 14.4 months (range, 3–48 months). Results: A total of 33 patients with symptomatic VADAs were reviewed, 23 of these patients with ruptured VADAs. The technical successful rate is 100% respectively in Willis covered stent (Group A) and SAC (Group B, n ​= ​20). The initial complete occlusion rate was significant higher in group A (100%) than group B (30%) (p ​ ​0.05). No obvious in-stent stenosis and no re-hemorrhage and delayed ischemic symptoms during the follow-up period. The final angiograms of all survived patients demonstrated the complete occlusion rate was higher in group A (100%) than group B (80%), but no significant statistical difference (p ​> ​0.05). Clinical outcomes were favorable in 31 (93.9%), severe disability occurred in one in group B, and only one death in group A. The final clinical outcomes were also not significant difference in the two groups (p ​> ​0.05). Conclusions: Our initial result demonstrated reconstructive EVT with Willis covered stent provides a viable approach for selected symptomatic VADAs involving the intracranial and extracranial segments, which is similar to favorable results with SAC. However, an expanded clinical experiences and larger cohort studies are needed.

Ni–Fe dissimilar butt joints (Inconel 718 and SUS316 sheets) were welded with an Ni-based filler metal using the cold metal transfer (CMT) process. The morphology of the joints was analyzed to elucidate the formation characteristics of the low-dilution-rate welding joints. The tensile strength of the joints was tested at different temperatures and with different macro morphologies to locate the weak area. The finite element method (FEM) was utilized to calculate the stress concentration of the Ni–Fe fusion line (FL) region at high temperatures. It was found that the stress was reduced and was not concentrated in the Ni–Fe FL region, if the WM reinforcement width was wider than 8 mm (original top gap of welding butt joint). The micro morphology and element distribution of the fracture surface and the interface cross section demonstrate that the interface of the Ni–Fe FL with insufficient diffusion is the region where the solidification crack occurs. Thus, this interface is the source of the FL crack and can substantially undermine the high temperature tensile properties of the joints. The metallurgical mechanism of solidification crack formation was also discussed by the phase diagram and solidus-liquidus temperature calculation. The surface of the solidification crack is Fe-based, indicating that it was formed during the melting and re-solidification of the SUS316 base metal surface. Furthermore, the formation temperature was higher than the initial solidification temperature of the welding metal.

In order to avoid decomposition of solid lubricants during laser processing and improve the lubrication stability of laser-clad self-lubricating coating, a novel multilayer structural WS2/NbC/Stellite 6 metal matrix self-lubricating coating (MMSC) with laser texturing layer (LTL), lubricant layer (LL) and laser-clad sealing layer (LSL) was fabricated on Cr12MoV steel via laser surface texturing (LST) and laser surface cladding (LSC) two-step process. The microstructure, phase and tribological properties of the multilayer structural MMCC were investigated by means of optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy, as well as dry sliding wear test in wide-temperature (room temperature, 200 °C, 400 °C, and 800 °C). Results show that the multilayer structure partially inhibited the decomposition of the lubricant so that WS2 particles retained in the coating and NbC promoted the formation of a new lubricating phase CrS in decomposed WS2. The multilayer structural coating prepared in two steps had lower friction coefficient (0.226) and wears volume (31.916 mm3) at room temperature (RT). Moreover, the friction coefficient of the multilayer WS2/NbC/Co-based self-lubricating coating was still low (0.306) at 800 °C, only. Adhesive wear was identified as the main wear mechanism and the discrepancies of tribological properties were found to be mainly dependent of the kind of lubricating films generated at the wear surface.

Accurate characterization of keyhole pool behavior is important to improve the penetration recognition and quality detection during the variable polarity plasma arc welding (VPPAW) of aluminum alloy. However, the low-level hand-crafted visual/acoustic features are often incapable of sufficiently representing the dynamic characteristics of keyhole pool under complex welding conditions. In this paper, we developed an end-to-end visual-acoustic penetration recognition (VAPR) framework based on a hybrid convolutional neural network (CNN) and extreme learning machine (ELM), which consists of three consecutive phases: (1) visual-acoustic data preparation, (2) multi-features extraction, and (3) penetration classification. Specifically, we applied a flexible dual-sensor acquisition system for synchronously collecting/preprocessing the visual-acoustic signals and exploring the internal correlation between the visual-acoustic features and keyhole pool behavior as well as weld penetration status. Then we established two individual CNNs for learning high-level visual-acoustic features directly from the raw visual images and 2-D time-frequency spectrograms. With the visualization of CNN-based deep learning features, we also explained the physical meanings of visual-acoustic features. To further improve the prediction performance of CNN model, we employed the ELM model as a strong tool to classify penetration status. By comparing with other state-of-the-art methods, our hybrid CNN-ELM approach with visual-acoustic fusion has a superior performance in terms of the classifying accuracy. The VAPR framework in this paper will provide some guidance for post-process quality inspection and realize an adaptive control of VPPAW process.

In-process penetration monitoring of the pulsed laser welding process remains a great challenge for achieving uniform and reproducible products due to the highly complex nature of the keyhole dynamics within the intense laser-metal interactions. The main purpose of this study is to investigate the feasibility of acoustic emission (AE) measurement for penetration monitoring based on acoustic wave characteristics and deep learning. Firstly, a series of laser welding experiments on aluminum alloys were conducted using high-speed photography and AE techniques. This allowed us to in-situ visualize the complete keyhole dynamics and elucidate the generation mechanism of acoustic waves originating from pressure fluctuations at the keyhole wall. Then, an adaptive time-frequency technique namely VMD (Variational Mode Decomposition) was proposed to characterize the acoustic energy distribution among the nine subsignals with low-frequency and high-frequency components under different welding penetrations. Lastly, a novel hybrid model combing CNN (Convolutional Neural Network) and LSTM (Long Short Term Memory) was designed to deeply mine the spatial and temporal acoustic features from the extracted frequency components. Extensive experiments demonstrate that our proposed approach yields a remarkable classification performance with a test accuracy of 99.8% and a standard deviation of 0.21, which obtains a high recognition rate. This work is a new paradigm in the digitization and intelligence of the laser welding process and contributes to an alternative way of developing an efficient end-to-end penetration monitoring system.

Inv(16)(p13.1q22) in acute myeloid leukemia (AML) is a common chromosomal abnormality. It leads to the core-binding factor ß-subunit (CBFβ)/smooth muscle myosin heavy chain 11 (MYH11) fusion gene. Different breakpoints were observed in the CBFβ gene at 16q22 and the MYH11 gene at 16p13.1. For this reason, different CBFβ/MYH11 fusion genes are generated, with more than 13 types having been reported to date. Type I CBFβ/MYH11 fusion transcripts are very rare, with only 10 cases being reported to date. This case report describes a primary AML patient with inv(16)(p13.1q22) and a rare type I CBFβ/MYH11 fusion gene. The morphological analysis did not conform to the typical M4eo. Abnormal eosinophils were less than 5%, and there was obvious dysgranulopoiesis. The patient was in hematological and genetic remission for 487 days after the initial chemotherapy cycles. However, the CBFβ/MYH11 fusion had been constantly positive. Moreover, the presence of non-type A fusions may affect its biology and clinical prognosis. Therefore, further studies on understanding its biological and prognostic significance are essential.

Abstract Background A novel phosphatidyl nanoprodrug system can be selectively released parent drugs in cancer cells, triggered by the local overexpression of phospholipase D (PLD). This system significantly reduces the intrinsic disadvantages of conventional chemotherapeutic drugs. However, the separation and purification processes of phosphatidyl prodrug, the precursor of phosphatidyl nanoprodrug, have not been established, and the preparation of nanocrystals with good stability and tumor-targeting capability is still challenging. Results In this study, we established a successive elution procedure for the phosphatidyl prodrug—phosphatidyl mitoxantrone (PMA), using an initial ten-bed volume of chloroform/methanol/glacial acetic acid/water (26/10/0.8/0.7) (v/v/v/v) followed by a five-bed volume (26/10/0.8/3), with which purity rates of 96.93% and overall yields of 50.35% of PMA were obtained. Moreover, to reduce the intrinsic disadvantages of conventional chemotherapeutic drugs, phosphatidyl nanoprodrug—PMA nanoprodrug (NP@PMA)—was prepared. To enhance their stability, nanoparticles were modified with polyethylene glycol (PEG). We found that nanoprodrugs modified by PEG (NP@PEG–PMA) were stably present in RPMI-1640 medium containing 10% FBS, compared with unmodified nanoprodrug (NP@PMA). To enhance active tumor-targeting efficiency, we modified nanoparticles with an arginine-glycine-aspartic acid (RGD) peptide (NP@RGD–PEG–PMA). In vitro cytotoxicity assays showed that, compared with the cytotoxicity of NP@PEG–PMA against tumor cells, that of NP@RGD–PEG–PMA was enhanced. Thus, RGD modification may serve to enhance the active tumor-targeting efficiency of a nanoprodrug, thereby increasing its cytotoxicity. Conclusions A process for the preparation and purification of novel phosphatidyl prodrugs was successfully established, and the nanoprodrug was modified using PEG for enhanced nanoparticle stability, and using RGD peptide for enhanced active tumor-targeting efficiency. These procedures offer considerable potential in the development of functional antitumor prodrugs.

The strong effects of Zn addition on the reaction in Sn/Cu systems are widely known. Nevertheless, the micro-mechanism for Zn accumulation behavior, phase evolution and void formation in Sn-xZn/Cu systems remain unclear. In this work, the effect of Zn addition on the interface behavior is investigated. Structures of Sn-xZn/Cu are prepared by the reaction between Sn-xZn solders (x = 0, 0.2, 0.5 and 0.8 wt.%) and the electroplated Cu (EP Cu) joints. During the thermal aging of Sn/EP Cu joints, many voids formed inside the Cu3Sn phase, especially close to the Cu3Sn/EP Cu interface. Whereas the voids were greatly suppressed with Zn addition. During the thermal aging, Zn gradually accumulated near the interface of IMCs/EP Cu. As thermal aging time to168 h and Zn content to 0.8 wt.%, Zn participated in the interface reaction, three layers with different contrasts, (Cu, Zn)6Sn5, Cu6(Sn, Zn)5 and (Cu,Sn)3Zn were formed. Theoretical analysis shows that Zn atom accumulated near the interface of IMCs/EP Cu due to lower diffusion energy barriers (Edf) of Zn than Cu atom. The preferential occupation of Zn atoms in Cu6(Zn,Sn)5 and (Cu,Zn)6Sn5 are Sn3 (4e) and Cu3 (4a) site because of the lowest lattice strain. The diffusion path interstice size for Cu atom via the IMCs layer gradually shrink with the increment of charge transfer in Zn-rich layers, corresponding the Edf of Cu atom gradually rise. As a result, the fluxes of Cu and Sn via the IMCs layer were balanced out, which reduced the Kirkendall voids formation. Keywords: Sn/Cu solder joint, Zinc, Accumulation behavior, Phase evolution, Kirkendall void

The weld penetration variation in laser-MIG hybrid welding under sensitive laser power range was investigated by welding experiments and CFD (computational fluid dynamics) simulation. During this investigation, joints of AH36 sheets were welded with varying laser powers by the laser-MIG hybrid welding process. In addition, the CFD model was established based on experimental parameters and measurement results. Moreover, surface tension, electromagnetic force, buoyancy, recoil pressure, evaporative condensation, evaporative heat exchange, melt drop transfer, and other factors were considered. The influence of various factors on molten pool depth and keyhole depth were studied, including temperature, velocity, and flow direction of liquid metal. The results show that the weld-forming effect is better at the laser power is 7.5 kW in the range of sensitive laser power. After the keyhole is formed, its depth gradually entered the stage of linear increase, oscillation increase, and oscillation balance. Increasing the laser power can effectively shorten the time of the two growth stages and allow the keyhole to enter the balance stage earlier. During the oscillation balance state of the keyhole, the molten metal under the keyhole flowed to the molten pool root in the reverse direction of welding; it can also promote weld penetration.

A three-dimensional heat transfer model for friction stir welding is presented in this paper. A moving coordinate was introduced to reduce the difficulty of modeling the moving tool. Heat input from the tool shoulder and the tool pin were considered in the model. The plastic deformation heat was introduced into the model, too. It is clear that the heat production increased owing to plastic deformation, and this process depends on the stress level. Temperature measurement experiments were done to validate the calculated results. The calculated results were in good agreement with the experimental results. Preheating the workpiece is beneficial to obtain a good weld seam.

The remote Laser spiral welding was utilized to zero-gap lap welding of galvanized steel. The relationship between pores in the weld zone and process parameters were investigated. The combination of high keyhole velocity and small spiral spacing was found to be essential for eliminating porosity in the weld area. As the spiral pitch decreases from 0.7 mm to 0.3 mm, the porosity decreases rapidly from approximately 20% to 0%. When the spiral spacing of 0.3 mm, the porosity reaches an acceptable quality level of less than 1%. The porosity tends to decrease as the keyhole velocity increases from 3 m min ^−1 to 9 m min ^−1 . At the spiral pitch of 0.3 mm and keyhole velocity of 9 m min ^−1 , the porosity in the weld area is almost completely suppressed. The peak shear strength of the spiral weld without porosity was 8819.8 N and the peak shear strength of the spiral weld with porosity was 5104.3 N. The tensile shear performance was increased by 72.8%. The low porosity caused by the spiral laser beam improves the tensile shear strength of the oscillating weld.

In this study, dissimilar butt joints were formed between as-rolled Inconel 718 and SUS 316 using cold metal transfer (CMT) with ERNiFeCr-2 filler metal at a welding speed of 5 mm s ^−1 and three different welding currents (130, 160 and 190 A). The morphology, microstructure, and mechanical properties of the joints and the mechanism by which the joint interface formed were studied. The results indicate that CMT welding parameters have an effect on the weld appearance and that the weld metal exhibits better wettability and spreadability at a welding current of 160 A. The interface between the weld metal and SUS 316 base metal was characterized by applying an optical microscopy (OM) and scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectrometry (EDS). The results revealed that no obvious diffusion of Ni and Fe ions was identified across the joint interface. The fractures that initiated in the joints during the tension testing formed in the heat-affected zone (HAZ) of the SUS 316 base metal, and the high-temperature tensile strength of the joint was observed to be 424 MPa, which is approximately 87.06% of that of SUS 316 base metal (487 MPa) and 67.19% of that of Inconel 718 base metal (631 MPa). In terms of the elongation, the joint (21.9%), Inconel 718 base metal (21.2%) and SUS 316 base metal (22.3%) elongations were similar. For comparison, the joint also was tested at room temperature, resulting in a tensile strength and elongation of 511 MPa and 27.5%, respectively. A spherical elemental Ni segregation morphology was clearly observed at the high-temperature fracture. Hardness studies demonstrated that the weld metal hardness is higher than that of the SUS 316 base metal.

In this work, the effects of electroplated Cu (EP Cu) and Cu addition (0.7%) in Sn solder on the intermetallic compounds (IMCs) growth and void formation were clarified by comparison with solder joints comprising of high purity Cu (HP Cu) substrate and pure Sn solder. After aging processes, a new IMC, Cu3Sn, was formed at the interface, in addition to Cu6Sn5 formed in the as-soldered joints. The EP Cu and Cu addition (0.7%) both had limited effects on the total IMCs thickness. However, the effects varied on the growth behaviors of different IMCs. Comparing to the void-free interface between Sn and HP Cu, a large number of voids were observed at the Cu3Sn/Cu interface in Sn/EP Cu joints. The formation of these voids may be induced by the impurities and fine grain, which were introduced during the electroplating process. The addition of Cu suppressed the inter-diffusion of Cu and Sn at the interface. Consequently, the growth of the Cu3Sn layer and formation of voids were suppressed.

Joining Al alloy to steel is of great interest for application in the automotive industry. Although a vast number of studies have been conducted to join Al to steel, the joining of Al to steel is still challenging due to the formation of brittle Fe–Al intermetallic compounds. In this work, the microstructure and mechanical properties of the dissimilar Al/steel joints with and without a nickel coating are comparatively investigated. A homogenous reaction layer composed of FeZn10 and Fe2Al5 is formed at the interface in the joints without Ni coating, and the joint facture load is only 743 N. To prevent the formation of brittle Fe2Al5, Ni electroplated coating is applied onto a steel surface. It has been shown that a nonhomogeneous reaction layer is observed at the interfacial region: Ni5Zn21 is formed at the direct irradiation zone, while Al3Ni is formed at the fusion zone root. The microhardness of the interfacial layer is reduced, which leads to the improvement of the joint mechanical properties. The average fracture load of the Al/Ni-coated steel joints reaches 930 N. In all of the cases, failure occurs at the Ni coating/fusion zone interface.

Three Ni-Cr-Si coatings were synthesized on the surface of copper by laser cladding. The microstructures of the coatings were characterized by optical microscopy (OM), X-ray diffraction (XRD), and scanning electron microscopy (SEM) with an energy dispersive spectrometer (EDS). According to the analysis results of phase compositions, Gibbs free energy change and microstructures, the phases of three coatings appeared were Cr3Si+γ-Ni+Cuss (Coating 1, Ni-26Cr-29Si), Cr6Ni16Si7+Ni2Si+Cuss (Coating 2, Ni-10Cr-30Si) and Cr3Ni5Si2+Cr2Ni3+Cuss (Coating 3, Ni-29Cr-16Si). The crystal growth in the solidification process was analyzed with a modified model, which is a combination of Kurz-Giovanola-Trivedi (KGT) and Lipton-Kurz-Trivedi (LKT) models. The dendrite tip undercooling in Coating 2 was higher than those of Coating 1 and Coating 3. Well-developed dendrites were found in Coating 2. A modification of Hunt’s model was adopted to describe the morphological differences in the three coatings. The results show that Coating 1 was in the equiaxed dendrite region, while Coatings 2 and 3 were in the columnar dendrite region. The average friction coefficients of the three coatings were 0.45, 0.5 and 0.4, respectively. Obvious plastic deformation could be found in the subsurface zone of Coatings 2 and 3.

The CrS/NbC Co-based self-lubricating composite coatings were successfully fabricated on Cr12MoV steel surface by laser clad Stellite 6, WS2, and NbC mixed powders. The phase composition, microstructure, and tribological properties of the coatings ware investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometer (EDS), as well as dry sliding wear testing. Based on the experimental results, it was found reactions between WS2 and Co-based alloy powder had occurred, which generated solid-lubricant phase CrS, and NbC play a key role in improving CrS nuclear and refining microstructure of Co-based composite coating during laser cladding processing. The coatings were mainly composed of γ-Co, CrS, NbC, Cr23C6, and CoCx. Due to the distribution of the relatively hard phase of NbC and the solid lubricating phase CrS, the coatings had better wear resistance. Moreover, the suitable balance of CrS and NbC was favorable for further decreasing the friction and improving the stability of the contact surfaces between the WC ball and the coatings. The microhardness, friction coefficient, and wear rate of the coating 4 (Clad powders composed of 60 wt % Stellite 6, 30 wt % NbC and 10 wt % WS2) were 587.3 HV0.5, 0.426, and 5.61 × 10−5 mm3/N·m, respectively.

The Ni-Ti-Si composite coatings were successfully fabricated on Ti6Al4V by laser cladding. The microstructure were studied by SEM (scanning electron microscopy) and EDS (energy dispersive spectrometer). It has been found that Ti2Ni and Ti5Si3 phases exist in all coatings, and some samples have TiSi2 phases. Moreover, due to the existence of these phases, coatings presented relatively higher microhardness than that of the substrate (826 HV (Vickers hardness)) and the microhardness value of coating 3 is about twice larger than that of the substrate. During the dry sliding friction and wear test, due to the distribution of the relatively ductile phase of Ti2Ni and reinforcement phases of Ti5Si3 and TiSi2, the coatings performed good wear resistance. The oxidation process contains two stages: the rapid oxidation and slow oxidation by high temperature oxidation test at 800 °C for 50 h. Meanwhile, the value of the oxidation weight gain of the substrate is approximately three times larger than that of the coating 4. During the oxidation process, the oxidation film formed on the coating is mainly consisted of TiO2, Al2O3 and SiO2. Phases Ti2Ni, Ti5Si3, TiSi2 and TiSi were still found and it could be responsible for the improvement in oxidation resistance of the coatings by laser cladding.