Statistical-experimental modeling of the effect of process parameters on geometric characteristics of laser cladding of stellite 6 on SS316 using second-order regression

Applications of 316 stainless steel can be developed by laser cladding of the Co-based superalloys, which has multiple enhancement properties and creates a small heat affected zone. Quantitive investigation of the effect of process parameters on geometrical features and providing reliable models to achieve the desirable metallurgical bond, minimal structural defects, and predicting the dimensions of the geometry without conducting excessive experimental tests are an important issue. This study evaluate the effects of the main process parameters of laser cladding on geometric characteristics of stellite 6 using the response surface methodology. A quadratic model was developed for each of the geometric characteristics. Laser power, scanning speed, and powder feed rate ranged between 400 and 600 W, 6–10 mm/s and 12–20 gr/min, respectively, were considered as the input variables and height, width, penetration depth and dilution were considered as responses. The experiments were designed using the box-behnken method. The accuracy and fitness of the models were evaluated using analysis of variance method. The results indicated the R2 factors obtained for height, width, penetration depth and dilution are equal to 0.89, 0.98, 0.98 and 0.96 respectively. After obtaining the desirability factor of 0.795, the optimal set of process parameters were selected as laser power of 510 W, scanning speed of 10 mm/s and powder feed rate of 13 gr/min. Verification of the optimization was done by performing experimental test,which maximum 13 % difference between actual values and the predicted values was obtained

Investigating the relationship between mechanical properties and residual stress in the laser cladding process of Inconel 625 superalloy

In the present study, the tensile strength, fracture surface, hardness, and amount of residual stress in Inconel 625 super alloy cladded with direct metal deposition (DLD) process in the states before and after stress relief was studied. Residual stresses on the cladding layer surface were determined via XRD method. According to results, the yield strength of Am sample increased by 10% compared to thecast sample (reference sample). Although the yield strength experiebced an increase, the ductility followed an opposite trend falling from 42.5% to 26%. According to residual stress test outcomes, tensile residual stress of 361 MPa in the additive-manufactured sample. After stress relaxation heat treatment and almost complete removal of residual stress, the ductility reached 52.5%, the ultimate strength was also improved by 17% from cast sample. Also, after stress relaxation, the hardness of the sample and its fluctuations are reduced

An investigation into the effect of scanning pattern and heat treatment on the mechanical properties of Inconel 718 in the direct metal deposition process

In this study, the additive manufacturing process of Inconel 718 superalloy on a homogenous forged substrate with three different patterns is investigated, followed by studying the samples’ mechanical properties and heat treatment effect on them. After additive manufacturing, the tensile properties of the samples were investigated by form of 50%-forging specimens and 50%-additively manufactured specimens. Results showed the best tensile properties are obtained in a sample made with a circular pattern. Also, the difference in the tensile properties of the sample made parallel to the tensile axis, and the sample created in the vertical direction indicate the anisotropic behavior of the additively manufactured samples. After additive manufacturing of samples with parallel, perpendicular, and circular patterns, the ultimate strength increased by 7, 6, and 11% compared to the control sample (forging). Despite the strength increase, the ductility of the specimens decreased by 28, 20, and 11% compared to forging specimen. In the 100%-additively manufactured sample, the ultimate strength increased by 6%, and the ductility decreased by 45%. After investigating the pattern for mechanical properties, annealing heat treatment at 1080 °C for 1 h and two aging processes at 620 and 720 °C for 4 and 8 h, respectively, were performed to improve the properties and create a strengthening phase. The ductility of the sample made with a 50% circular pattern and 50% forging sample increased by 51% and 36% by annealing compared to the raw state and the control sample, respectively. Moreover, the hardness level and ductility became uniform and increased after annealing

Microstructural investigation of direct laser deposition of the Ti–6Al–4V alloy by different melt pool protection conditions

Titanium alloys require a special protecting atmosphere during the fabrication process due to their strong affinity with oxygen and nitrogen elements at high temperatures. In this study, the effects of different protection conditions on microstructure, phase characteristics, interstitial elements absorption and microhardness of additively manufactured Ti–6Al–4V alloy by direct laser deposition method have been investigated. Fabrication of specimens with similar laser parameters was carried out in three different protection conditions consist of air, closed box and argon shower. Characterization of samples was performed by utilization of OM, SEM, XRD, inert gas fusion method, micro-hardness and tensile strength analysis. Results indicated that fabrication of samples in an air atmosphere without proper protection leads to 2.5% spherical porosities, TiO2 and TiN formation in top layers, changing the c/a ratio from 1.59 to 1.61, absorption of 1870 and 500 ppm oxygen and nitrogen and 155 HV increment in micro-hardness value. Also, uncommon semi-globular microstructure in different locations of samples has been observed. The special protective atmosphere provided by argon shower led to 6.3% spherical porosities, negligible lattice parameter variation and martensite microstructure formation. It was found that in the optimal protection condition that was provided by a closed box, the typical basketweave microstructure with less than 1% porosity and 960 and 140 ppm oxygen and nitrogen absorption were achieved, which did not exceed the standard limits. In addition, the mechanical properties of UTS tensile strength, yield strength and elongation, were obtained 1042, 893 MPa and 13.2% respectively

Evaluating laser surface melting of NiCrAlY-APS coating and its effect on high-temperature oxidation behavior of NiCrAlY/YSZ thermal barrier coating before and after surface melting

This research study was conducted to investigate the laser melting parameters of NiCrAlY-APS coating. High-temperature oxidation was investigated using yttria partially stabilized zirconia (YSZ) ceramic coating. Also, the oxidation behavior of the TBC coating was investigated and studied before to and after laser surface melting of the NiCrAlY coating. Microstructural characterization was done using a scanning electron microscope (SEM), elemental analysis by energy dispersive spectroscopy (EDS), and phase analysis by X-ray diffraction (XRD). Surface melting was then performed in the power range of 150–300 W and scanning speed of 2–6 mm s−1. Surface melting was also conducted on the coating using two strategies: single-pass and multi-pass. The obtained results showed that the average melting depth and thickness reduction were directly related to the laser power, while they had an inverse relation with the laser scanning speed. Furthermore, multi-pass surface melting parameters reduced porosity to less than 0.1 %. Roughness measurements also showed a decrease in the coating's surface hardness after surface melting, as compared to the APS coating. The structure consisted of oriented columnar dendrites after melting the laser. The adhesion strength of the TBC coating and laser surface melting coating was at 41 MPa and 53 MPa, respectively. After 200 h of oxidation in the G1504 sample, the TGO layer's growth was decreased; due to the growth of a single oxide layer, it had better oxidation resistance in comparison to the other sample