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Online process monitoring and quality control has been a long-standing challenge for variable polarity plasma arc welding (VPPAW) due to the inherent instability and fluctuation of the keyhole molten pool. This work developed an innovative welder intelligence-enhanced deep random forest fusion (WI-DRFF) approach, aiming to describe the dynamics of front-side molten pool and accurately predict the weld penetration. Based on the human welder’s prior knowledge, we firstly proposed an image processing algorithm to extract the low-level handcrafted features, which could quantitatively describe the geometrical appearance of the keyhole. Afterwards, we constructed a convolutional neural network (CNN) to learn the high-level discriminative features of weld pool and interpret the physical characteristics of the deep features with visualization. Finally, we incorporated the handcrafted keyhole features and deep features to concatenate a multi-level feature vector for predicting the weld penetration based on random forest (RF) classifier. Extensive experiments demonstrate that our proposed approach yields a remarkable classification performance comparing with state-of-the-art machine learning algorithms even with limited training data. This approach is a new paradigm in the digitization and intelligence of welding process and can be exploited to provide a feedback in an adaptive quality control system.

The TaC/TiC/Stellite X-40 Co-based composite coatings with different contents were successfully cladded on a Cr-Zr-Cu alloy substrate. The microstructure, wear and corrosion resistance of the compo...

Wire arc additive manufacturing (WAAM) is a novel manufacturing technique by which high strength metal components can be fabricated layer by layer using an electric arc as the heat source and metal wire as feedstock, and offers the potential to produce large dimensional structures at much higher build rate and minimum waste of raw material. In the present work, a cold metal transfer (CMT) based additive manufacturing was carried out and the effect of deposition rate on the microstructure and mechanical properties of WAAM Ti-6Al-4V components was investigated. The microstructure of WAAM components showed similar microstructural morphology in all deposition conditions. When the deposition rate increased from 1.63 to 2.23 kg/h, the ultimate tensile strength (UTS) decreased from 984.6 MPa to 899.2 MPa and the micro-hardness showed a scattered but clear decline trend.

In order to estimate Weibull parameters in the Weibull statistical fracture theory as truly material properties independent of specimen geometry and loading mode, first the Weibull statistical fracture theory is transformed into the ordinary Weibull distribution function under certain approximation. Then the standardized format of ordinary Weibull distribution is introduced to enable Weibull modulus as the single parameter for estimation via the maximum likelihood method. The method of using standardized Weibull distribution for strength data synchronization and Weibull modulus estimation is validated by analyzing extensive strength data sets measured from uniaxial flexure, biaxial flexure and their combination, and from smooth and notched specimens. The technical path to estimate the scale parameter and threshold strength as material properties in the Weibull statistical fracture theory and effect of sample size on the estimation accuracy are also discussed.

The effects of different vibration frequencies on the microstructure, laves phases and microvoids of Inconel 718 weld joints were investigated in this research by using the laser welding combined with mechanical vibration. The results demonstrated that the application of vibration significantly suppressed the growth of columnar crystals, reduced the formation of carbides, and refined the microstructure. With the increase of the vibration frequency, the mechanical vibration stayed prominent. The molten pool was subjected to the pressure and vibration of the metal liquid, which expanded the depth and the width of the weld. Applying vibration could reduce the amount of Laves phase, and it is found that with the increase of vibration frequency, the morphology of Laves phase could change from granular to strips, as found during the experiment. The welds with 522 Hz vibration frequency had the smallest Laves phase size and the largest average microhardness value of 331 HV. At the vibration frequency of 1331 Hz, the amount of Laves phases was the least, and it was distributed in a miscellaneous manner in the form of granules and stripes. However, increasing the vibration frequency could not effectively reduce the number of microvoids in the weld.

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.

Aluminum alloy 6061 was welded with zinc coated low carbon steel by cold metal transfer (CMT). The microstructure composition, morphology and growth process of the welding joint and the HAZ were researched. The weld area on the side of the galvanized steel sheet mainly contains Fe2Al5. And on the side of the aluminum alloy substrate, it is mainly filled with a needle-like FeAl3. At the same time, Al8Fe2Si is formed at the edge of FeAl3. The zinc-rich region on the side of the aluminum alloy mainly contains an aluminum-zinc solid solution and an aluminum-zinc co-crystal, and the current size had no significant effect on the type and morphology of the compounds produced in the interface layer.

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.

“Weibull statistics” for strength distribution analysis refers to either the ordinary Weibull distribution function or the Weibull statistical fracture theory. The ordinary Weibull distribution function is an empirical distribution function on an equal footing with other type of classical empirical distributions such as normal and log-normal distributions for fitting the statistical data of various random variables nonexclusive to materials strength. It has no explicit physical meaning and cannot be used for size scaling and prediction of strength. The Weibull statistical fracture theory is a weakest-link statistical fracture model for a solid with the strength distribution of an elemental volume being described by the ordinary Weibull distribution function. It has the capability of size scaling and prediction of strength for specimens with different geometries and different loading modes. The three-parameter Weibull statistical fracture theory in uniaxial flexure of prismatic beams is reformulated and validated by both numerical and real strength experiments of different ceramics.

Vibration-assisted laser welding experiment of 5052 aluminum alloys was carried out to focus on the influences of vibration parameters on microstructure and fatigue fracture. The experiment found that the vibration process homogenized the microstructure and promoted the formation of fine equiaxed grains significantly. In addition, vibration made the hardness uniform by reducing the area of the fusion zone. Experimental results of double welds showed that residual stress reduced by 58 to 77% under the action of micro-vibration. Vibration frequency and vibration acceleration had significant effects on the longitudinal and transverse residual stress, respectively. Under the same fatigue load condition, the average fatigue limits of the base metal (BM) and the welded joints were 160 and 120 MPa, respectively. Under the conditions of 107 cycles, the maximum fatigue strength of the welded joints has reached 74.95% fatigue strength of the BM. Vibration-assisted laser welding could obviously improve the fatigue performance and increase the fatigue life of the welded joints, which was a potential way to improve the quality of welded joints.

The mechanical properties of 2060 and 2099 T-joints welded by double-sided laser beam welding were analyzed in this experiment. Various mechanical tests were performed to determine the transverse tensile properties of the region perpendicular to the weld, the tensile properties of the skin and stringer, the compressive properties of the region parallel to the weld seam, and the fatigue properties perpendicular to the weld seam. The T-joint was found to consist of the base metal, partial melting zone, equiaxed zone (EQZ), columnar crystal zone, and cellular dendritic zone from the base metal to the center of the weld seam. The EQZ was proved to be the weak area during mechanical properties tests of the T-joint. Moreover, the welding penetration had a great influence on the transverse tensile properties and weak areas were located in the EQZ near the lower fusion line. The EQZ near the upper fusion line was the weak area in the process of compression. In addition, severe porosities and cracks greatly influenced the mechanical properties of the joint. The fatigue property was closely related to the deformation angle; the fatigue source was located at the weld toe, and the crack propagation was along the base metal.

Cold metal transfer plus pulse (C + P) arc was applied in the additive manufacturing of 4043 Al alloy parts. Parameters in the manufacturing of the parts were investigated. The properties and microstructure of the parts were also characterized. Experimental results showed that welding at a speed of 8 mm/s and a wire feeding speed of 4.0 m/min was suitable to manufacture thin-walled parts, and the reciprocating scanning method could be adopted to manufacture thick-walled parts. The thin-walled parts of the C + P mode had fewer pores than those of the cold metal transfer (CMT) mode. The thin- and thick-walled parts of the C + P mode showed maximum tensile strengths of 172 and 178 MPa, respectively. Hardness decreased at the interface and in the coarse dendrite and increased in the refined grain area.

There are mainly two kinds of laser used in welding of materials, continuous laser beam welding (CLBW) and pulsed laser beam welding (PLBW). The two kinds of laser welding have each welding characteristics. Compared with CLBW, the heat input of PLBW can be controlled lower, and has been widely used in the connection of thin plate materials. Since the pulse shaping can be edited to realize the preheating and slow cooling of each welding process, pulsed laser has been studied to suppress hot cracks and other defects in the field of aluminum alloy, magnesium alloy and other materials welding. This article describes the application of pulsed laser in alloy welding. The main welding problems and prevention methods were summarized. By discussing the index had been proposed to predict the sensitivity of solidification cracks, the formation and growth processes of hot cracks in pulsed laser welding was more comprehensively analyzed. Finally, the outlook for the future trends of pulsed laser welding is presented.

Phase stability, elasticity, hardness and relevant electronic structures of M nB m (M = Ni, Cr, Mo, W, n = 23,5,3,1, m = 6,3,2,1) binary borides have been investigated by first-principles calculati...

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

Cobalt-based self-lubricating coatings with the addition of NbC and h-BN were prepared by means of laser cladding on a die steel (Cr12MoV) substrates, aiming at their implementation in metal forming applications involving demanding friction reduction and anti-wear. The effect of different amounts of h-BN with constant content NbC (30 wt%) on the microstructure of the laser-clad Stellite 6 alloy was probed through measures of XRD, SEM, EDS and EBSD. Microhardness, wear properties, and antifriction mechanism of the self-lubricating coatings were also discussed as well. The results proved that with an increase in h-BN content, in addition to NbC phase with polygonal shape observed in the h-BN-free Stellite 6/NbC coating, Nb(C, B) interstitial compounds having multiple grain orientations were formed in inter equiaxed crystal regions. Following the microstructural characterization, the tribological behavior and micro-hardness were analyzed. The results exhibit considerably better anti-friction properties of Stellite 6/NbC/h-BN coating compared to subtract and its excellent tribological performance could be reflected by data of friction test. The lubrication effect of h-BN is proved by the reduction in coefficient of friction. Meantime, the addition of NbC helps in improving micro-hardness and anti-wear. The NbC solidification-growth was detailly discussed in the paper.

Three Ni-Mo-Fe-Si quaternary metal silicide alloy coatings were fabricated on the pure nickel plate by laser cladding. The mixed powders of different compositions of Ni, Mo, Fe, and Si elements were employed as the cladding materials. X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and electron backscattering diffraction were adopted to investigate the microstructure. The wear properties of three coatings were evaluated under large contact load at room-temperature, dry-sliding wear-test conditions. Results indicated that the phases of three coatings were Ni3Si2/Ni2Si/Mo2(Ni, Fe)3Si as matrix phases and Mo2(Ni, Fe)3Si/Mo6Ni5Si2 as primary phases, Ni3Si2/γ-(Ni, Fe)+Ni31Si12/γ-(Ni, Fe) as matrix phases and Mo2(Ni, Fe)3Si/Mo6Ni5Si2 as primary phases, and γ-(Ni, Fe) as the matrix phase and Mo2(Ni, Fe)3Si as the primary phase for Coatings 1, 2, and 3, respectively. For quaternary metal silicide alloys, ideal configurational entropy of Ni-Mo-Fe-Si alloys increased as the composition tends to equimolar ratio. High entropy will reduce the kinds of phases and be easy to form phases with simple structure in Ni-Mo-Fe-Si coatings. The solubility of Fe element in Mo2(Ni, Fe)3Si phase is high because of the its replacement of Ni in this complicate phase. The average micro-hardness for Coatings 1, 2, and 3 is 987 HV, 977 HV, and 734 HV, respectively. Three coatings exhibited outstanding wear resistance due to a combination of excellent strength and toughness.

TiN reinforced Ni matrix composite coating with in-situ synthesized TiS lubricant phase were fabricated on Ti-6Al-4V alloy by laser cladding with NiCrBSi, TiN and WS2 powder mixtures. The phase compositions, microstructure, microhardness and tribological behaviors are investigated by X-ray diffractometer (XRD), scanning electron microscope (SEM) with energy dispersive spectrometer (EDS) as well as a multi-functional Tribometer. Effect of WS2 contents on the microstructure, microhardness and tribological properties were studied. And the corresponding wear mechanism was discussed. Results indicate that the hardness of the coating (about 900HV0.2) is significantly improved compared with substrate (370HV0.2). Coefficients of friction and wear rates of these coatings have been significantly reduced. Besides, laser-clad coating using the mixed powders of 50%Ni-30%TiN-20%WS2 has good anti-wearing and friction reducing effects, and the main wear mechanisms of that are abrasive wear and micro-plowing.

Iron-based amorphous alloys have received extensive attention due to their high hardness, elastic modulus/limit and wear/corrosion resistance. In this research, an attempt has been made to develop an amorphous coating of Fe-Cr-Mo-C-B-Y metallic glass coating on the steel substrate through laser surface treatment. During the test, various process parameters are used to determine the position of the amorphous phase. After coating, the microstructure and phase distribution of the coating were analyzed by scanning electron microscope, X-ray diffraction and transmission electron microscope. Mechanical properties of the coating were analyzed by using microhardness testing, abrasion resistance and nanoindentation methods. The results show that the coating thickness varies directly with the incident laser power and interaction time. The microstructure of the coating can be divided into three layers: the first layer (columnar crystals), the second layer (the crystalline phase filled with the unit structure) and the third layer (the unit structure consists of a crystalline phase and an amorphous phase). As the heat input of laser cladding decreases, the volume fraction of the amorphous phase increases, and the average microhardness and nanohardness increase.

The effects of minor Cu (0.7%), Ag (3.5%) and Ni (0.1%) additions in Sn solder on the interfacial transfer and phase evolution were clarified in Sn/Cu solder joints. (Cu,M)6Sn5 and (Cu,M)3Sn (M = Cu, Ni) layers were observed at the Sn/Cu interface during thermal aging at 150 °C. The additions of Cu, Ag and Ni alloy elements were found to change the growth of the Cn–Sn intermetallic compounds (IMCs). The results showed that Cu, Ag and Ni additions were able to suppress the growth of (Cu,M)3Sn (M = Cu, Ni) layers, but promoted the (Cu,M)6Sn5 growth. This was because the reactions on the (Cu,M)6Sn5 side were promoted by the refined IMCs grain size, whose growth was at the expense of (Cu,M)3Sn. In addition, the interfacial transfer rate (thickness ratio, y) of (Cu,M)3Sn/(Cu,M)6Sn5 versus the thermal aging time (t) was found to be close to parabola relationship, the y increased gradually with the alloy elements from Ni, Cu to Ag. The phase evolution (η′-Cu6Sn5, η-Cu6Sn5, e-Cu3Sn, Ag3Sn, η′-(Cu,Ni)6Sn5, η-(Cu,Ni)6Sn5 and e-(Cu,Ni)3Sn) at the interface between Cu and Sn solder doped with minor Cu, Ag and Ni was also elucidated.

A crack-free Fe-Cr-Mo-C-Y-B amorphous coatings has been prepared on the surface of Q235 steel by the method of magnetic-field-assisted laser cladding. The uniformity of the distribution of elements in the coating is increased by alternating the magnetic field, which increases the plastic toughness of the coating. The mechanical behaviour of indentation points after nanoindentation of the coated sample was observed by transmission electron microscopy.

The hot cracking sensitivity dramatically increases because of the longitudinal macro-segregation of craters and the transverse macro-segregation of welding center in pre-layers. Statistical analysis of the total area, average size and Nb concentration of interdendritic low-melting point Laves phase, the Nb concentration of the γ phase in the dendritic core, and the arm spacing of different sub-regions was used to explore the effects of macro- and micro-segregation of Nb. Solidus and liquidus curves were used to determine the temperature at which solid and liquid phases coexist in different sub-regions, which were combined with Scheil equation curves to identify Nb sources and interlayer transfer, so as to develop a model for the molten pool of subsequent layers. This model explains the effect of transversal and longitudinal macro-segregation in the pre-layer on the Nb concentration of the melt pool of subsequent layers, the dynamic balance of the solidification interface and the relative area of Laves phase in the macro-segregated sub-region of the solidified metal.

The macro-structure, microstructure and mechanical properties of 4043 aluminium-alloy parts manufactured by variable polarity cold metal transfer welding (CMT + Advance) have been investigated. The...

A vacuum brazing process using BNi7+3% Cu composite solders to braze Cr18-Ni8 steel was carried out. The joint can be divided into three zones: Isothermally Solidified Zone (ISZ), Athermally Solidified Zone (ASZ) and Diffusion Affected Zone (DAZ). The characteristics of microstructure were observed by scanning electron microscope (SEM). The element distribution in the Cr18-Ni8 steel brazed joint and the content of elements in the organizations were measured by energy dispersive spectrum (EDS). The brazed joints are mainly composed of FeNi3 phases, Ni solid solutions, Ni3P eutectic structures and Cr-Ni-P compounds. The effects of different factors on the microstructure and properties were studied. The growth rate of solid solution increased first and then decreased with the rise of temperature. The hardness of diffusion zone increased first and then decreased when the brazing temperature went up. Cu played an important role to increase the hardness of brazing seam. Prolonging holding time or reducing the brazing gap width was beneficial for the formation of the solid solution. The hardness increased with the extension of holding time. The brazing gap had little effect on hardness. The fracture mode of the joint was ductile fracture. The joints had higher strength when the brazing temperature increased.

Nano-Ni encapsulated h-BN/Ni-based alloy (Ni60) self-lubricating composite coatings on a medium carbon steel were fabricated by laser cladding using two types of lasers: a 5 kW continuous wave (CW) CO2 laser and a 400 W pulsed Nd:YAG laser, respectively. A high-energy ball milling method was adopted to clad nano-Ni onto nano-h-BN with an aim to enhance the compatibility between the h-BN and the metal matrix during laser cladding processing. The microstructure, phase structure and wear properties of the self-lubricating composite coatings were investigated by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD), as well as dry sliding wear testing. The research indicated that laser cladding of the self-lubricating composite coatings demonstrates sound cladding layers free of cracks and porosities. It was found that a reaction between h-BN and Ni-based alloy occurred, which generated hard phase CrB and Ni3B leading to the increasing of the microhardness of the coatings by CO2 laser cladding, while laser molten pool suppressed h-BN floating up to upper regions of coating for lower temperature and rapid solidification by YAG laser cladding. The high energy ball milling of nano-Ni onto nano-h-BN significantly improved the interfacial compatibility between h-BN and Ni60 matrix. The friction coefficient of the laser-clad Ni60/nano-Ni encapsulated h-BN coating was reduced obviously.

The KF-2-WC-CaF2 Ni-based self-lubrication coatings were synthesized on the surface of 6061 aluminum alloy with preset powder by laser cladding / friction stir processing (FSP). OM, SEM, EDS and XRD were used to characterize the phase constituents, microstructure and properties of the coatings, and the micro-hardness distribution and wear properties were also analyzed. The results showed that smooth and good metallurgical bonding zone is formed between the coating and the substrate. The microstructure of the one-stepped coating is dendrite, cell crystal, columnar crystal and equiaxed crystal. The main phase constituents of the two-stepped coating consist of α-Ni, α-Al, AlNi3, Al3Ni2, WC and CaF2. And the micro-hardness is significantly higher than that by direct laser cladding. With the increase of distance between coating and stirring tool, mechanical effect gradually weakened, micro-hardness curve and friction coefficient showed a gradient feature along the thickness direction.

It is difficult to collect the crack propagation signal under general continuous welding condition due to other signal interference of molten pool. In order to study the effect of residual stress on crack propagation, acoustic emission technology was successfully applied to monitor welding process according to the characteristics of pulsed laser welding. Crack free welding is achieved by reducing the pulse interval to limited the crack size of single pulse welding spot. The welding process was monitored synchronously by high speed photography and acoustic emission, the evidence of crack propagation after solidification of weld is successfully captured.

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.

Solidification crack was a common welding defect in welding of aluminum alloy. When solidification shrinkage and heat shrinkage of the vulnerable zone and its surrounding solids were hindered, it will cause grain boundary cracking owing to insufficient supply of liquid metal. Therefore, cracks generally appear in the middle part of aluminum alloy welding spot at the late stage of solidification. Compared with continuous laser, pulsed laser could meet more precise heat input control and was widely used in aluminum alloy sheet welding. In this research, by designing different pulse shaping to improve the solidification condition of the 5083 aluminum alloy pulsed laser welding spot, the numerical simulation was used for analyzing the solidification rate and temperature gradient of molten pool. Application of ramp-down pulse decreased crack cross-sectional area from 420475 µm2 to 0, and step-down pulse could also effectively control the crack radius. The results showed that effect of suppressing solidification crack on the horizontal direction of the welding spot was obvious to the vertical direction. Using ramp-down or step-down pulse shaping also reduced the volume of the liquid molten pool at the end of the laser process, which decreased the shrinkage stress at the late stage of solidification.

TaC/Stellite X-40 Co-based composite coatings were fabricated on nickel‑aluminum bronze (NAB) substrates by laser surface cladding (LSC), aiming at improving wear and corrosion resistances of NAB in marine environments. The morphology, microstructure, microhardness, wear and electrochemical corrosion behaviors of the surface treated composite coatings were studied. The results showed uniform distribution of carbide and intermetallic reinforcements such as TaC, Cr3C2 and Co3Ta in γ-Co matrix which lead to improvements of resistances to wear and electrochemical corrosion. Microstructural analyses of the LSC coating containing 20 wt% TaC showed the presence of fine reinforcements with isocellular crystals in the surface region and refined columnar crystal near the substrate area, as well as metallurgical bonding between the LSC coating and the NAB substrate. With the increase of TaC content in the cladding powders, the number of the granular reinforcements in the LSC coatings increased gradually, and the particles became larger. The maximum average microhardness of the composite coating of 20 wt% TaC was about 771.7 HV0.2, which is approximate 6.2 times higher than that of the NAB substrate (125.1 HV0.2). The minimum average coefficient of friction (COF) of the composite coatings was about 0.303 and its wear rate was about 0.4 times that of the NAB substrate. The self-corrosion potential (-0.182) of the composite coating with 20 wt% TaC was significantly higher than that of the substrate (-0.298), and the current density was lower, which implies that the corrosion resistance of the coating was significantly improved.

Stellite 12 and Ti/B4C composite coatings were successfully fabricated on the surface of 304 stainless steel substrates by laser cladding. The effect of Ti/B4C with different mass fractions on the structure and properties of Stellite 12 coating were studied. The properties and the growth mode of the coating were analyzed. The results show that the Stellite 12 coating was mainly composed of face-centered cubic γ-Co and Cr7C3. With the addition of Ti/B4C, TiC submicron particle phase was synthesized in situ in the coatings. Residual B4C as a heterogeneous nucleus particle, forming a submicron microstructure TiC/B4C strengthening phase, and the particle size gradually decreases. The TiC/B4C particles can refine the grains of the coatings. The micro-hardness of the coating gradually increased with the increase of Ti/B4C, and the highest were 650 HV. The wear resistance and oxidation resistance of the coatings gradually increased with the increase of Ti/B4C.

An ultrafast laser was used to ablate the surface of stainless steel. Periodical surface micro-textures including micro-grooves, micro-pits and micro/nano-ripples were successfully fabricated. As a typical reactive wetting system, Al-Si alloy was used to study the wetting and spreading behaviors on the laser patterned surfaces of stainless steel. The results showed that initial, rapid spreading and gradient balance stages were found in the spreading process. By comparing to the primitive surface, Al-Si alloy exhibited worse wettability on the surface with micro-grooves and micro-pits because of the geometrical characteristics and nano-scale oxides residuals after laser processing; however, Al-Si alloy showed better wettability on the surface with micro/nano-ripples owing to the formation of micro/nano hierarchically patterns and the resultant improved capillary actions. The interfacial reaction layer formed during wetting and spreading processes were also investigated. The surface micro-textures were found to enhance the interfacial metallurgical reactions, thus increasing the thickness of the reaction layer. This work provides a new method to improve the wettability, spreadability and metallurgical reactions of Al-Si/stainless steel reactive wetting system and may extend its use in other reactive wetting systems. This method may be able to improve brazing, soldering, coating and other processes involving solid/liquid interfacial interactions.

In the work the in-situ synthesis of Ti3SiC2 (MAX) phase and silicide reinforced Ni-based composite self-lubricating coatings from Ti-Si-C system and NiCrBSi powders were carried and initiated by laser cladding with use of 5 kW fiber laser beam with 3 mm spot. The microstructures of the laser-clad in situ synthetic self-lubricating coatings were analyzed by a scanning electron microscope (SEM) equipped with an X-ray energy dispersive spectrometer (EDS). An X-ray diffraction (XRD) spectrometer and an electron back-scattered diffraction (EBSD) were used for determination of the reaction products in the composite coatings. The friction and abrasion behavior of the coatings were evaluated at room temperature by a dry sliding friction tester. The results indicate that in-situ chemical reactions took place between elements Ti, Si and C in the laser molten pool, and the reaction products included Ti3SiC2, Ti5Si3, and TiC ceramics as well as TiNix compound. Finally, three laser-clad Ti3SiC2/Ti5Si3/TiC/Ni-based composite coatings with the total thickness about 1 mm were fabricated on Ti6Al4V alloy. The average microhardness of the three coatings was 703.2 HV0.2, 751.9 HV0.2 and 850.6 HV0.2 respectively, which has been significantly improved, compared with the hardness of Ti6Al4V substrate (about 360 HV0.2). The average friction coefficient of the Ti3SiC2/Ti5Si3/TiC/Ni-based composite coating (50 wt% Ni25/50 wt% Ti-Si-C) reduced to 0.33 at room temperature, and it exhibited the wear rate of 13.5 × 10−5 mm3 N−1 m−1. The laser cladding Ti3SiC2/Ti5Si3/TiC/Ni-based composite coatings characterized by small amount of adhesive wear, plastic deformation and relatively smooth wear surface could be observed.

In this work, laser cladding has been employed for the preparation of nickel-based self-lubricating coating NiCrAlY/Ag2O/Ta2O5 on Inconel 625 alloy substrate. In order to study the evolution of Ag2O and Ta2O5 in the coating and its effect on the microstructure, three coatings of NiCrAlY/Ag2O, NiCrAlY/Ta2O5 and NiCrAlY were prepared for comparison. The composition and microstructure of the powders and the corresponding composite coatings were studied by SEM-EDS and XRD. The average hardness of Coating (A, B, C, D) and substrate is 369.5 HV, 300.7 HV, 306.5 HV, 332.1 HV, and 246.8 HV, respectively. The friction and wear properties of the self-lubricating coating were studied by MFT-5000 multifunctional friction and wear tester at RT (room temperature) ~750 °C. In order to compare with the self-lubricating coating, the same friction and wear test was done on the substrate under the same condition. It can be seen that the friction coefficient of the self-lubricating coating from RT to 750 °C is 0.64, 0.23, 0.62 and 1.5 times lower than that of the substrate, and its wear rate is 2.03, 2.11, 2.82 and 1.04 times lower than that of the substrate, respectively. SEM-EDS and XRD were used to analyze the morphology and composition of the worn surface. It can be seen from the results that Ag is the main lubrication phase at room temperature, and NiO and Ag work together to lubricate at 350 °C. When the temperature reaches 550 °C, Ag loses its effective lubrication, while the wear-resistant glaze layer composed of NiO and CrO2 provides the main lubrication. At 750 °C, AgTaO3 and Ag2Ta4O11 formed by in-situ reaction will act as a synergistic lubrication with the wear resistant glaze layer composed of oxide. The synergistic lubrication of Ag, NiO, CrO2, AgTaO3 and Ag2Ta4O11 enables self-lubrication of the composite coating in a wide temperature range.

Inconel 718 alloy laser-welded joints have poor mechanical properties due to the presence of Laves phases and liquation cracks. This paper intends to solve the above problems by high-frequency micro-vibration-coupled bead-on-plate laser welding. According to the shape of the weld beam, the upper part of the weld is defined as the nail head, and the lower part is the nail body. The results showed that high-frequency micro-vibration can achieve grain refinement. The micro-vibration could break the primary dendrite arm to form secondary dendrite and reduce epitaxial growth of the cellular crystal region. Micro-vibration exacerbated the flow of Niobium (Nb) elements surrounded by dendrites and reduced dendritic segregation, which decreased the formation of Laves phases. The combination of interdendritic Nickel (Ni), Titanium (Ti), and Nb and the precipitation of strengthening phases &gamma, &prime, and &gamma, &Prime, were promoted. When the vibration acceleration was 50.10 m/s2, it could inhibit the formation of Laves phases among dendrites and the size of the bulk Laves phase was effectively reduced. The cracks generated in the Inconel 718 alloy were distributed at three locations including the nail-head, the nail-body, and the junction of nail-head and nail-body. When the vibration frequency was 919 Hz, the length of the liquation crack reduced from 180 to 110 &mu, m. While under 1331 Hz, the expansion of the liquation crack was extended, with the length of 200 &mu, m.

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.

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&ndash, 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.

A novel magnetic g-C3N4 (Fe3O4-g-C3N4) was prepared in one step and used to removal Cd (II) from aqueous solution. VSM, FT-IR, SEM, laser particle analyses and XRD were used to character Fe3O4-g-C3N4. The kinetic data was more descibed by Peseudo-second-order model. Langmuir model to describe isotherms data is more convincing and the predicated maxmium adsorption capacity for Cd (II) is 204.5 mg/g.

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.