Wear Tribo-Performances of Laser Cladding Colmonoy-6 and Stellite-6 Micron Layers on Stainless Steel 304 Using Yb:YAG Disk Laser

N. Jeyaprakash,Che‑Hua Yang,Sheng‑Po Tseng 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.6

Stainless steel material has been widely used in aeronautical, chemical and nuclear industries due to good corrosion resistance. However, the material has less hardness and wear resistance. In this study, two various depositions namely Colmonoy-6and Stellite-6 have produced on 304 Stainless steel. Besides, the coating was examined to reveal their metallurgical, mechanicaland tribological properties. In addition, wear mechanism, wear debris and roughness averages were studied. The outcomesindicate that both coatings show with dendrite structure due to rapid cooling rates. Hardness of the clad surface has improvedthan substrate material. The results of friction coefficient of specimen with Colmonoy-6 is lower than that of specimensStellite-6 and substrate. Also, wear resistance of Colmonoy-6 has increased 49 times than substrate sample, which revealsthat Colmonoy-6 laser cladding plays role on wear resistance. Adhesive and abrasive are the major wear mechanisms in thepresent study.

Microstructure and Tribological Behaviour of Inconel-625 Superalloy Produced by Selective Laser Melting

N. Jeyaprakash,Che‑Hua Yang,G. Prabu,R. Clinktan 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.12

This research discusses the comparative investigation of the Inconel-625 superalloy manufactured by Selective Laser Melting(SLM) process and conventional process. The fabricated component was investigated to reveal the phase transformations,microstructural features and nano-hardness. Further, wear test was conducted on specimens manufactured by both themethods as above, to study the tribological properties. XRD analysis showed that the SLM specimen has more intensity at(111) diffraction peak than the other two specimens and that the solid solution of γ-(Ni, Cr, Fe) (FCC) phases grew at (111),(2 0 0) and (220) planes. The Inconel-625 powder had lattice parameters 0.3592 nm, 0.3116 nm and 0.3012 nm, whereasthe SLM specimen possessed the lattice parameters 0.3599 nm, 0.3121 nm and 0.3012 nm which were higher than the othertwo specimens. The microstructure analysis confirmed the presence of consistent and homogeneously equiaxed cell in theconventional alloy, whereas the SLM specimen possessed heterogeneous columnar structure. Along with the columnar cell,some equiaxed and cellular cell were also formed in the SLM specimen due to remelting of the overlapped region. Moreover,the formation of equiaxed cell in XY, YZ and ZX plane directions of the conventional alloy specimen and columnar cell inthe SLM specimen was confirmed through Electron backscatter diffraction (EBSD) analysis. The SLM-produced specimenexhibited higher nano-hardness due to the formation of angular columnar cell, fine hard phases, effective bonding strengthand defect-free surface. Abrasive wear mechanism played an important role in both the samples. The wear rate of the conventionalInconel-625 alloy specimen was around 4.58 × 10–3 mm3/m while it was 1.83 × 10–3 mm3/m. The worn-out surfaceof the SLM specimen produced a lower roughness average compared with the conventional Inconel-625 specimen. Thus, theSLM technique is a promising and predominant technique to develop nickel-based superalloys for frictional applications.

Correlation of Microstructural Evolution with Mechanical and Tribological Behaviour of SS 304 Specimens Developed Through SLM Technique

N. Jeyaprakash,Che‑Hua Yang,K. R. Ramkumar 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.12

This research work focuses on the development of SS 304 specimens using the selective laser melting technique and analysesthe microstructural modifications. Further, it correlates the evolution of microstructure with mechanical properties likemicrohardness, nanoindentation and tribological behaviour. The conventionally prepared as-cast SS 304 specimens were takenfor comparison of the results obtained with the SLM technique. The diffraction pattern obtained from x-rays disclosed theabsence of δ phase and confirmed that refinement of grains occurred in the structural level through decrease in the intensityof α peaks. Optical micrograph witnessed that the grains were in micron and sub-micron size. SEM images depicted thepresence of columnar and cellular sub-grains within a grain which were in ultrafine level. The microhardness and nanoindentationresults obtained for the SLM specimen were almost multiple times higher than the conventional as-cast specimens. There was a significant improvement in the wear resistance in the SLM specimens than the conventional as-cast specimens. From the results, SLM is found to be a favourable technique to manufacture metallic components in a way to obtain a goodservice life of engineering components.

Microstructural Evolution and Wear Behavior of AlCoCrCuFeNi High Entropy Alloy on Ti–6Al–4V Through Laser Surface Alloying

G. Prabu,Muthukannan Duraiselvam,N. Jeyaprakash,Che‑Hua Yang 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.7

AlCoCrCuFeNi high entropy alloy particles were laser surface alloyed on Ti–6Al–4V substrate to improve the tribologicalproperties. The microstructure, phase formation and hardness improvement of the laser alloyed surface were examined. Thewear resistance of the laser alloyed specimen were evaluated through pin-on-disc apparatus and compared with substratespecimen. The wear mechanism of the worn-out surface and roughness were studied. The laser alloyed specimen exhibitsdual solid solution along with the BCC phase. The alloyed region shows dendrite and interdendrite structure with equiaxedgrain formation. The hardness of laser alloyed region is 3 times higher than the substrate material due to dominant BCC phaseformation. The laser alloyed specimen shows higher wear resistance compared to substrate due to solid solution strengtheningand intermetallic formation. The wear resistance of the laser alloyed specimen was 2.62 times than the substrate at 50 N loadand 0.9 m/s sliding velocity. Abrasive, adhesive wear and severe plastic deformation were observed in the substrate specimen, whereas in the laser alloyed specimen mild abrasive wear was observed. The laser alloyed specimen has 0.56 times thecoefcient of friction of the Ti–6Al–4V substrate at 50 N load and 0.9 m/s sliding velocity due to self-lubrication propertyof HEA elements. Surface roughness of worn-out laser alloyed specimen was 0.44 times that of the Ti–6Al–4V substrate.

Evaluation of Defect Detection in Aluminium, CFRP and Epoxy Resin Plates Using Non-contact Air-Coupled Ultrasonic Waves

Leslie Bustamante,N. Jeyaprakash,Che-Hua Yang 한국정밀공학회 2020 International Journal of Precision Engineering and Vol.21 No.10

In the fi eld of aerospace materials and structures, water coupled ultrasonic testing was not desirable due to changes in properties and contamination reason. Therefore, in the present study non-contact air coupled ultrasonic transducers were proposed as an alternative examination for such applications. This present study describes our practical knowledge of using piezoelectric air-coupled transducers for visualization and defect identification of aluminium, CFRP and epoxy-resin specimens. Further, the effectiveness of the system is verified by experiments conducted in the inspection of artificial defects and 2D images was reconstructed through scanning of specific specimen surface. Results show that, all the created defects were identified successfully using C-scan technique. The measured defect values were compared with experimental defect values and shows good agreement. The 1 MHz piezoelectric transducer was the best for all the three specimens which is used in the present study because of the material structure being evaluated. The bulk wave piezoelectric transducer was identified as extensive pulse attenuation by the structure of the aluminium, CFRP and epoxy resin.

Evaluation of Fatigue Damage in Steel Plates Through Non-linear Ultrasonic Technique

Che-Hua Yang,N. Jeyaprakash,Shan-Yan Wu 한국강구조학회 2023 International Journal of Steel Structures Vol.23 No.5

Under the action of repeated stress on the components such as turbine blades, springs, crankshafts, biomedical transplantation, and load components, the strength of the material is reduced or the material is damaged. These components continue to be subjected to different types of tension, compression, bending, vibration, thermal expansion, and contraction or other repetitive stress effects. These stresses are often lower than the yield strength of the material, but must be greater than the fatigue limit of the material. The stress can cause the dislocation substructure of the material, thereby changing fatigue failure. In this study, we mainly used non-linear ultrasonic measurement to generate high-energy waves, made it incident on the steel and received its double-frequency signal at the other end. Then we calculated the non-linear factor of steel based on the ratio of the double frequency amplitude to the square of the fundamental frequency amplitude. Besides, the non-linear factor of steel was measured under different fatigue cycles. Then, the curve of the material non-linear factor was determined and the cycle stress number was measured by the relationship between different fatigue cycles and their non-linear factors. The final results show that, with the increase in the number of applied cyclic stresses, the non-linear factor also tends to increase. The non-linear factor of the test piece with no damage at all and the test piece with one million fatigue damages can be up to 6.5%. Non-linear ultrasonic technique was successfully implemented to analyse the fatigue damages.

Effect of α-Al and Si Precipitates on Microstructural Evaluation and Corrosion Behavior of Laser Powder Bed Fusion Printed AlSi10Mg Plates in Seawater Environment

Periyakaruppan Murugesan,V. Satheeshkumar,N. Jeyaprakash,Che‑Hua Yang,Sundara Subramanian Karuppasamy 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.9

AlSi10Mg is a hypoeutectic alloy that has remarkable characteristics and implemented in diverse areas. Most of theAlSi10Mg parts are fabricated via traditional processes. The AlSi10Mg parts made by these processes have coarsermicrostructure, reduced mechanical behaviors, and minimum lifespan. This study is aimed at manufacturing the AlSi10Mgparts by Laser Powder Bed Fusion (LPBF) process followed by analyzing their mechanical properties. The microstructureevolution was examined from the micrographs of Optical Microscope (OM), Field Emission Scanning Electron Microscope(FESEM), Electron Backscatter Diffraction (EBSD), and Transmission Electron Microscope (TEM). Tafel, Nyquist, Bodeand surface plots were used to determine the corrosion resistance and surface roughness at different intervals. FESEMmicrographs revealed the existence of bimodal equiaxed α-Al grains containing Si phase as their grain boundaries. Aftersolidification, the secondary precipitates (Mg2Si) were segregated in the printed sample which accounts for enhancing themechanical characteristics. More grain growth and textures were noticed along the building direction of the sample andthis direction exhibits higher hardness compared with the scanning direction. Further, TEM analysis confirmed that theformed microstructure is rich in equiaxed α-Al with Si eutectics. Corroded X-ray Diffraction (XRD) plot showed that themaximum intensity of MgAl2O4is observed at 25 h immersion test sample. Among the various samples, 25 h LPBF sampleprovides significant resistance toward corrosion based on the values of current density, polarization resistance and averagesurface roughness. This is due to the formation of stable passive film on its surface thereby providing better anti-corrosioncharacteristics.