Microstructure Of Cladding Research Articles

Preliminary Experimental Study of Laser Cladding Repair on Directionally Solidified Blades

There is large use of directionally solidified superalloy blades in aerospace, but the repair of these blades is a real problem. The laser cladding technology is able to implement the repair. The experiments in this paper study the microstructure of laser cladding, analyze the formation mechanism and control method, implement the directional growth of microstructure in multilevel laser cladding layer, and provide a theoretical and experimental basis of laser cladding repair on directionally solidified superalloy blades.

Low-loss 3D-laser-written mid-infrared LiNbO3 depressed-index cladding waveguides for both TE and TM polarizations.

We report mid-infrared LiNbO3 depressed-index microstructured cladding waveguides fabricated by three-dimensional laser writing showing low propagation losses (~1.5 dB/cm) at 3.68 µm wavelength for both the transverse electric and magnetic polarized modes, a feature previously unachieved due to the strong anisotropic properties of this type of laser microstructured waveguides and which is of fundamental importance for many photonic applications. Using a heuristic modeling-testing iteration design approach which takes into account cladding induced stress-optic index changes, the fabricated cladding microstructure provides low-loss single mode operation for the mid-IR for both orthogonal polarizations. The dependence of the localized refractive index changes within the cladding microstructure with post-fabrication thermal annealing processes was also investigated, revealing its complex dependence of the laser induced refractive index changes on laser fabrication conditions and thermal post-processing steps. The waveguide modes properties and their dependence on thermal post-processing were numerically modeled and fitted to the experimental values by systematically varying three fundamental parameters of this type of waveguides: depressed refractive index values at sub-micron laser-written tracks, track size changes, and piezo-optic induced refractive index changes.

Morphology-Dependent Hardness of Cr7C3-Ni-Rich Alloy Composite vs Orientation Independent Hardness of Cr7C3 Primary Phase in a Laser Clad Microstructure

Microstructural evolution with superheating was studied in chromium carbide-nickel coatings deposited by laser cladding. At lower superheating, selective growth of 〈0001〉 direction from the high density of Cr7C3 grains nucleated resulted in a columnar structure with (0001) texture. Increased superheating lead to the loss of columnar structure as well as the (0001) texture. The hexagonal Cr7C3 showed an unusual isotropic nanoindentation hardness evidently correlated with its low c/a ratio. However, the rod-like morphology of the carbide dendrites resulted in significant anisotropy in the hardness of the composite.

Experimental Characterization of Clad Microstructure and its Correlation with Residual Stresses

The repair of dies and molds used in the automobile industry by laser cladding (LC) is an important and emerging trend in additive manufacturing (AM) today. LC provides an alternative to the traditional deposition techniques which are ad-hoc and imprecise for powder metallurgical steels used in the repair of these components. The current study focuses on understanding the correlation between microstructure and the residual stress developed due to the deposition process. The microstructure was characterized using Electron Backscatter Diffraction (EBSD) analysis and the residual stress was measured using micro focus X-ray diffraction technique. The EBSD study revealed that the relative difference in martensite phase fraction resulted in local grain misorientations. A thermomechanical finite element (FE) model was also developed to predict the magnitude and nature of residual stresses in the component. The FE model calculated the stress field by considering only the thermal strain developed between the clad and substrate layers. The FE model was able to capture the nature of residual stresses in the clad and substrate where the thermomechanical effects dominate. The study revealed the importance of incorporating the effect of metallurgical transformation in FE model to accurately predict the residual stress variation in the substrate region.

Precompensation of the thermal-induced refractive index changes into a fully aperiodic LPF for heat load resilience.

In this paper, a strategy consisting of precompensating the thermal-induced transverse refractive index changes is undertaken to push further the appearance threshold of a multimode regime. First, a standard air-silica large pitch fiber (LPF) and a fully aperiodic large pitch fiber are confronted in regard to their heat load resilience and capabilities for single-mode emission. Thereafter, slight refractive index depressions are judiciously introduced into the active core area. This approach enhances the delocalization of the high-order modes even under severe heat load levels. This combination of aperiodic cladding microstructuration and index-precompensation theoretically increases the multimode regime threshold while preserving large mode field areas. This investigation is performed at 1.03 and 2 μm operating wavelengths.

Direct laser cladding of layer-band-free ultrafine Ti6Al4V alloy

Abstract Ti6Al4V alloy was fabricated on pure titanium substrate using laser cladding. The effect of scanning speed on microstructure, hardness and wear performance of the Ti6Al4V cladding was investigated. The layer-band-like zone, which consists of coarse basket-weave microstructure with short-lamellar α phase and β phase, decreases with the increase of scanning speed. Layer-band-free cladding is obtained at a high scanning speed. With the increase of the scanning speed, the microstructure of the cladding evolves from lamellar or lath-like α/α′ phase to refined acicular α/α′ phase. The ultra-fine microstructure with submicron scaled acicular α/α′ phases (60–400 nm in width) and β phase is obtained under the scanning speed of 600 mm min − 1 . The clad exhibits a high hardness of 7.6 GPa, a high elastic modulus of 136.4 GPa, a reduced friction coefficient of 0.46 and a low wear loss of 0.5 mg in dry sliding wear tests. The main worn mechanisms are fatigue and abrasive wear. A rational high scanning speed is beneficial to the enhancement of wear performance of the Ti6Al4V cladding, due to the obtained ultra-fine microstructure, high residual stress, high hardness and fatigue strength.

Improved microstructure and mechanical properties of dissimilar explosive cladding by means of interlayer technique

Aluminium and copper plates are explosively cladded with Al 5052, copper and SS 304 interlayers and the results are reported. While continuous molten layer is obtained in conventional explosive clads, a smooth interface, devoid of defects, is obtained in interlayer laced explosive clads. The mechanical properties of interlayer laced explosive clads confirm higher kinetic energy utilization leading to stronger clad. Ram tensile, shear strengths and Vickers microhardness of Al–Cu explosive clad with different interlayers are higher than conventional two layer clad.

Study of dilution in laser cladding of a carbon steel substrate with Co alloy powders

High power diode laser with coaxial powder injection was used to deposit single tracks of cobalt alloy on to a carbon steel plate in order to study dilution. Two different methods to evaluate dilution are proposed and validated: dilution results to be proportional to the average percent or iron present in the clad. To study the correlations between dilution and processing parameters, clads were produced in different processing conditions. Dilution is correlated with the specific energy, and equation to estimate the average iron contamination of the clads was found. ‘Trial and error’ method was applied to improve this estimation. A statistically better prediction of the iron contamination is obtained when the combined parameter P2.5/F4 is used. Dilution influences clad microstructure and thus hardness of the final coating, which decreases on increasing dilution. Phase distribution is also affected by dilution, Fe and C contamination stabilises α-fcc phase.

Processing and characterization of composite cladding through microwave heating on martensitic steel

The composite wear resistant cladding of nickel-based powder matrix and 10% SiC powder as reinforced was developed through microwave hybrid heating on martenisitic stainless steel (SS-420) substrate. The development of the clad has been carried out by using a domestic microwave applicator of frequency 2.45 GHz and 900 W power level. The microstructural and mechanical characterizations of the developed clad were carried out by using scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and Vicker’s microhardness analysis. Results revealed that clads of approximately 1.25 mm thickness were developed with significantly low porosity (∼1.10%). The scanning electron microscopic results show that the microstructure of clad exhibits typical cellular-like structure. The metallurgical bonding between clad and substrate surface was obtained with partial dilution. The complex carbides of chromium and silicides of chromium, iron, and nickel phases were identified in the clad region by XRD study, which may enhance the Vicker’s microhardness of the clads significantly. The average Vicker’s microhardness of the developed clad was in the range of 652 ± 90 HV.

Influence of Hydrogen Content on Microstructure and Mechanical Properties of Zr1Nb Fuel Cladding after High-Temperature Oxidation

The aim of this study is to investigate the influence of hydrogen on the microstructure and mechanical properties of Zr1Nb fuel cladding after high-temperature oxidation. As-received or pre-hydrided materials were tested. The influence of different cooling rates was examined as well. The microstructure was observed using of light microscopy. Oxygen distribution was measured using X-ray microanalysis. Local mechanical properties were determined by the microhardness and nanohardness measurements. Ring compression testing (RCT) was employed with the aim to obtain the macroscopic mechanical properties. Fractographic analysis was performed after the RCT. The experimental results confirmed that hydrogen as well as the cooling rate substantially influenced the microstructure and affected both local and macroscopic mechanical properties.

Stress evaluation of laser cladding coating with critically refracted longitudinal wave based on cross correlation function

Research on stress evaluation of laser cladding coating with critically refracted longitudinal wave was introduced in this paper. Two critically refracted longitudinal wave transducers with 5MHz frequency, spacing between which was constant, were employed as signal emitter and receiver. Based on acoustoelastic equation deduction, relationship between the difference in time of flight and tensile stress is obtained. Combing with cross correlation theory, the difference in time of flight between stressed and unstressed critically refracted longitudinal signals was calculated. Results show that stress evaluation is affected by layer interface and anisotropic microstructure of laser cladding coating, precision of stress evaluation of laser cladding coating increases as step length increases until it attains one cycle. In addition, influence of waveform distortion caused by microstructure of laser cladding coating on stress evaluation is discussed. At last, verification test is carried out and the experimental result is well consistent with theoretical result.

Microstructure, magnetic properties and empirical electron theory calculations of laser cladding FeNiCr/60%WC composite coatings with Mo additions

FeNiCr/60%WC coatings were deposited by laser cladding with direct injection of FeNiCr+60%WC powder premixed with different amounts of Mo powder (0–4wt.%) onto the N1310 nonmagnetic steel. The morphology was characterized using a scanning electron microscope (SEM), the phase analysis was performed using an X-ray diffractometer (XRD), and the magnetic properties were examined using a vibrating sample magnetometer (VSM). The empirical electron theory (EET) of solids and molecules was used to calculate magnetic moments of Fe3W3C and Ni3Mo3C. The relative permeability of FeNiCr/60%WC composite coatings containing different amounts of Mo ranged from 1.008 to 1.052, which was significantly lower than that without Mo addition (1.104). The relative permeability decreased with increasing Mo content until a minimum was reached, and then increased with further increasing Mo content. Ni3Mo3C phase was formed initially at high Mo addition (≥2.5%) due to the metallurgical reaction between the Mo particles and the Fe-based alloys. Both Ni3Mo3C and Fe3W3C phases were weakly ferromagnetic with a magnetic moment of 0.6816 and 0.9018 respectively, which seemed to be the main factors affecting the non-magnetic properties of the cladding coatings.

Experimental characterization of laser cladding of CPM 9V on H13 tool steel for die repair applications

H13 tool steel with excellent hot working properties is commonly used for manufacturing dies. However, the damage of die surface due to cyclic thermo-mechanical loading is detrimental to the service life. In order to enhance the die life, it has been observed that cladding based repair is superior to welding or thermal spraying repair techniques. In this paper, experimental study of laser cladding of H13 has been carried out. CPM 9V steel powder has been deposited on H13 tool steel plate for repairing the die surface damage using a CW CO2 laser in conjunction with powder injection system. The effect of laser parameters on clad geometry and clad quality has been investigated. The microstructure of laser cladded samples has been characterized using optical microscope (OM) and scanning electron microscope (SEM). The phases and the residual stresses present in the clad have been determined via X-ray diffraction. The micro-hardness profiles obtained in the clad–substrate system and the hardness change due to cyclic thermal loading have also been characterized. Optical micrographs of the clad microstructure shows existence of vanadium carbide particles embedded in martensite and retained austenite. The hard vanadium carbide particles increase the clad hardness to an average of four times greater than the substrate hardness. It has been observed that compressive residual stresses are generated in clad which is desirable for repair applications as it will impede the crack propagation resulting in enhanced die life.

Real-time control of microstructure in laser additive manufacturing

A novel closed-loop process is demonstrated to control deposition microstructure during laser additive manufacturing (LAM) in real-time. An infrared imaging system is developed to monitor surface temperatures during the process as feedback signals. Cooling rates and melt pool temperatures are recorded in real-time to provide adequate information regarding thermal gradients, and thus control the deposition microstructure affected by cooling rates during LAM. Using correlations between the cooling rate, traveling speed, and the clad microstructure, a novel feedback PID controller is established to control the cooling rate. The controller is designed to maintain the cooling rate around a desired point by tuning the traveling speed. The performance of the controller is examined on several single-track and multi-track closed-loop claddings in order to achieve desired microstructures with specific properties. Results indicate that the closed-loop controller is capable of generating a consistent controlled microstructure during the LAM process in real-time.

An Experimental Study of Microstructure and Mechanical Behavior of Alloy 625 Weld Overlay Deposited On ASTM A516 Grade 70

Background/Objectives: Surface modification for protection against corrosion is a critical field of research in the oil and gas industry. Alloy 625 is a superalloy with excellent resistance to pitting and corrosion. Methods/Statistical Analysis: Alloy 625 weld overlays were cladded through GTAW process on A516 carbon steel. The welding current ranging from 230 - 240 A the welding voltage 11 - 13 V; welding polarity EN (-). After welding, optical and SEM observations were conducted to determine the changes in the microstructure of base metal and clad. For examination of mechanical strength of claddings shear test was performed in accordance with ASTM A265 standard. Results: After Optical microscopy examinations, two different microstructures were observed in the HAZ zone. In the base metal, the grain size was reduced during the manufacturing process. The microstructure of weld metal was austenitic with dendritic structure. EDX observation showed that precipitates were mainly Niobium carbide (NbC). In the HAZ near the clad, microstructure included acicular ferrite, widmanstatten pattern, bainite, and pearlite. The tensile strength of a clad interface can be an important Consideration. For examination of mechanical strength of claddings shear test was performed in accordance with ASTM A265 standard. The minimum shear strength of different samples was 210 and 255 Mpa, which is higher than what it is stated in ASTM A265 standard. Conclusion/Application: The results showed that the manufacturing parameters in welding result in an appropriate mixing between base metal and clad material. The shear strength is higher than base metal and acceptable.

Anisotropic structure affects thickness measurement of laser cladding coating with surface ultrasonic wave based on cross-correlation function

Thickness evaluation of laser cladding coating with surface ultrasonic wave method was introduced in this research. Two surface ultrasonic wave transducers with 5 MHz frequency, distance between which was constant, were employed as signal emitter and receiver. Based on cross-correlation theory, the difference in time of flight between surface ultrasonic signals corresponding to different coating thickness was calculated. The relationship between the difference in time of flight and coating thickness is obtained. The results show that coating thickness evaluation is affected by microstructure of laser cladding coating, and accuracy of coating thickness evaluation increases as step length increases until it attains one cycle. In addition, influence of waveform distortion caused by microstructure of laser cladding coating on coating thickness evaluation is discussed. At last, verification test is carried out and the error is in the allowance range.

Effect of heat treatment on microstructure and residual stress fields of a weld multilayer austenitic steel clad

Samples of ferritic–perlitic steel were cladded by submerged arc welding with three layers of two austenitic stainless steel filler metals. After the weld cladding, samples were submitted to stress relief heat treatment (SRHT) under different parameters. The characterization of the microstructure of the samples was made by optical and scanning electron microscopy, and the residual stresses determined by X-ray diffraction and incremental hole drilling method. The results were compared and related to the SRHT conditions. The microstructure of the third layer of the as-welded clad consists of cellular austenite and intercellular eutectic delta-ferrite particles, while the microstructure of the first layer presents a high proportion of lathy martensite in γ-Fe cells. The second layer contains a low proportion of martensite and high proportion of austenite. The SRHTs induced partial decomposition of delta-ferrite in the superficial layer, increasing the rate of decomposition with the treatment temperature, and the coarsening of precipitates in the vicinity of the interface carbon steel–stainless steel. The superficial layer of the as-welded and machined clad plate presented residual compressive stresses. The SRHT at 540°C, for 10h of holding time, enabled some residual stress relaxation, unlike the treatment at 620°C, during 1h, which increased the compressive stresses.

Effect of CeO2 and Y2O3 on microstructure, bioactivity and degradability of laser cladding CaO–SiO2 coating on titanium alloy

To solve the lack of strength of bulk biomaterials for load-bearing applications and improve the bioactivity of titanium alloy (Ti–6Al–4V), CaO–SiO2 coatings on titanium alloy were fabricated by laser cladding technique. The effect of CeO2 and Y2O3 on microstructure and properties of laser cladding coating was analyzed. The cross-section microstructure of ceramic layer from top to bottom gradually changes from cellular–dendrite structure to compact cellular crystal. The addition of CeO2 or Y2O3 refines the microstructure of the ceramic layer in the upper and middle regions. The refining effect on the grain is related to the kinds of additives and their content. The coating is mainly composed of CaTiO3, CaO, α-Ca2(SiO4), SiO2 and TiO2. Y2O3 inhibits the formation of CaO. After soaking in simulated body fluid (SBF), the calcium phosphate layer is formed on the coating surface, indicating the coating has bioactivity. After soaking in Tris–HCl solution, the samples doped with CeO2 or Y2O3 present a lower weight loss, indicating the addition of CeO2 or Y2O3 improves the degradability of laser cladding sample.

电-磁复合场协同作用对激光熔覆层凝固组织的调控研究

电-磁复合场协同作用对激光熔覆层凝固组织的调控研究

레이저 클래딩 공정 조건이 코발트 합금-텅스텐 카바이드 혼합 코팅층의 균열 발생에 미치는 영향

In this study, cracking susceptibility of laser cladding was investigated according to the processing parameters such as laser power, scan speed and feeding rate with blended powders of stellite#6 and technolase40s(WC+NiCr). The solidification microstructure of clad was composed of Co-based dendrite structures with γ+Cr7C3 eutectic phases at the dendritic boundaries. The crack propagation showed transgranular fracture along dendritic boundaries due to brittle chrome carbide at the eutectic phases. From results of fractography experiments, the fracture surface was typical cleavage brittle fracture in the clad and substrate. The number of clad cracks, caused by a tensile stress after the solidification, increased with increase of laser power, scan speed and feeding rate. Increase of the laser power caused large pores by facilitating WC decarburizing reaction. And the pores affected increase of crack susceptibility. High scan speed caused increment of clad cracks due to thermal stress and WC particle fractures. Also, increase of the feeding rate accompanied an amount of WC particles causing crack initiation and decarburizing reaction.