MICROSTRUCTURE OF NiCrBSi/WC COMPOSITE COATING DEPOSITED ON AISI316 STAINLESS STEEL BY TIG COATING PROCESS

It is aimed to investigate the coating of AISI316 stainless steel with NiCrBSi/WC at different ratios using TIG method. In this study, the Ni-based WC-reinforced MMC layer was manufactured by the TIG composite coating method, and then the microstructure of the coating layer was examined. Microstructure and phase components of the composite coatings were characterized by optical microscopy, scanning electron microscopy, and X-ray diffraction. A metallurgic bound was found between the coating layer and the substrate through the TIG coating process. WC was re-solidified in the matrix by dissolving with high input energy. Several phases were found, including Ni-rich ([Formula: see text]-Ni) primary dendritic phase, Ni-Ni3B, and Ni3Si eutectic structure, Cr7C3, Cr2B3, Cr3Ni2, Ni2W4C, and Ni[Formula: see text]W3 phases in dendritic structures. The presence of carbides in the structure had affected the hardness of the coating. The maximum hardness value was found to be 469.5 HV and the hardness of the coating layers was increased at least 2.5 times compared to that of the substrate material.

Microstructural Characteristics and Mechanical Properties of a Nb/Nb5Si3 based Composite with and without Directional Solidification

The Nb/Nb5Si3 based composites were fabricated by conventional casting (CC) and directional solidification (DS) methods. Micro structural characteristics, compressive properties and fracture toughness of the CC and DS composites were investigated by SEM, XRD, TEM, bending and compression tests. The results demonstrate that in the CC Nb/Nb5Si3 based composite, the intergrowth of fine (Nb,Ti)ss and α-(Nb,Ti)5Si3 phases leads to the formation of eutectic structure and the coarse α-(Nb,Ti)5Si3 dendritic phase prefers to grow along eutectic cell boundary. The (Nb,Ti)3Si, (Ti,Nb)5Si3 and Dy2O3 phases mainly segregate along the eutectic cell boundary and moreover there is an orientation relationship between the (Nb,Ti)3Si and (Nb,Ti)ss phases: [001] (Nb,Ti)3Si//[112](Nb,Ti)ss and (110)(Nb,Ti)3Si//(110)(Nb,Ti)ss. The DS processing promotes the formation of coarse primary α-(Nb,Ti)5Si3 phase, (Ti,Nb)5Si3/(Nb,Ti)ss eutectic and α-(Nb,Ti)5Si3/(Nb,Ti)ss eutectic in the DS Nb/Nb5Si3 based composite. Moreover, the (Nb,Ti)ss and α-(Nb,Ti)5Si3 phases are aligned paralleling to the DS direction and exhibits strong crystal orientation preference. In addition, an orientation relationship between the (Nb,Ti) ss and α-(Nb,Ti)5Si3 phases is observed: [310]α(Nb,Ti)5Si3//[110](Nb,Ti)ss. Compared with the CC Nb/Nb5Si3 based composite, the DS Nb/Nb5Si3 based composite possesses the higher yield strength and fracture toughness, which should be ascribed to the microstructure optimization.

Microstructure and Wear Properties of FeCrC, FeW and Feti Modified Iron Based Alloy Coating Deposited by PTA Process on AISI 430 Steel

The plasma transferred arc (PTA) process was used for developing wear resistance of AISI 430 steel substrate. Appropriate quantities of FeCrC, FeW and FeTi powders were combined to create conditions that synthesized M7C3 particles into reinforced Fe-based composite surface coating. The phase transformations on new created coated surfaces were comprehensively examined by using a combination of scanning electron microscopy (SEM), microanalysis by energy dispersive spectrometry (EDS), X-Ray diffraction (XRD), microhardness and abrasive wear tests. The microstructure studies of the superficial layers of the coating revealed presence of a mixture of the dendritic phase structure of austenite (γ) and fine eutectic M7C3 carbides. The results show that; the concentrations of the elements (Cr, W, Ti) added as ferroalloys, the size of dendrites formed in the coated surface, the change of hardness of the coated surfaces, the carbide volume rate and thickness of the coating changed by the variation of the processing parameters (ratio of reinforcement particulates and heat input).

Microstructure Evolution and Mechanical Properties of Suction Cast Ti60Fe40-xCox (x = 0, 16, 18, 20, 22, 24) Alloys

The present work is aimed at understanding the microstructure evolution in a series of Ti60Fe40-xCox (x= 0, 16, 18, 20, 22, 24) alloys. The ternary alloys are synthesized by arc melting cum suction casting technique under high purity argon atmosphere to obtain alloy cylinders having 3 mm diameter and aspect ratio of 17:1. Detailed X-ray diffractometry and electron microscopic studies are carried out to identify the phases in the investigated alloys. It has been found that the alloys consist of fine scale eutectic matrix between bcc (b-Ti)ss and Ti(Fe,Co) phases along with the dendritic phase of Ti(Fe,Co), whereas the dendritic phase of Ti2(Fe,Co) has also been observed for x = 16 and 20. It is also found that ternary Ti60Fe20Co20 alloy shows good combination of compressive strength (~2507 MPa) and plasticity (~16.3 %) among the investigated alloys.

High Anticorrosive Properties of Hot-Dip 55 wt% Al-Zn-Si Coatings on Q235 Steel

A comparative study of the morphology and anticorrosive behaviour of commercial 55 wt% Al-Zn-Si coatings (CC) and hot-dip 55 wt% Al-Zn-Si coatings (HD) on Q235 steel was performed by using surface analysis techniques and electrochemical measurements. Despite the ingredients of the Al-rich dendritic phase for HD coating similar to the ingredients for CC coating, aluminum content in the Zn-rich phase for HD coating was almost twice higher than aluminum content for CC coating. The difference of surface morphologies and chemical compositions in Zn-rich phases for the two 55 wt% Al-Zn-Si coatings could significantly affect their corrosion properties. The corrosion behavior of the two coatings was investigated in 0.01 mol L-1 NaCl + 0.01 mol L-1 NaHSO3 aqueous solution. Both polarization curve and electrochemical impedance spectroscopy results indicate HD coatings had much higher corrosion resistance than CC ones.