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Ni60A/WC composite coating reinforced with ZrB2/ZrC was layered on GTD-111 superalloy by laser cladding. The effect of an ultrasonic field on coating formation, microstructure, microhardness, and wear was investigated and analyzed. The results showed that the resulting coating had pores and microcracks, which were removed when using an ultrasonic field. Ultrasonic fields increased the heat input and increased the dimensions of the coating pool by creating a cavitation effect. The dendrites of the coating microstructure were mainly composed of Zr(B, C) and ZrC blocks and small α-Zr dendrites. The mechanical vibrations resulting from the application of ultrasonic fields caused the crushing of the growing dendrites, and as a result, the grains and dendrites crumbled. By decreasing the grain size, the average hardness increases from 312 HV for coating without an ultrasonic field to 617 HV for coating with 300 W ultrasonic power. The results of the wear test also showed that the sample coated with 300 W of ultrasonic power, with a coefficient of friction of 0.41 and scar wear of 6.8 µm, has the highest wear resistance due to the removal of porosity and the presence of equiaxed grains on the top and bottom of the clad zone. [ABSTRACT FROM AUTHOR]

In the present study, ZrB2 nanoparticles were synthesized using sol-gel method. Zirconium alkoxide was used as the source of zirconium and boric acid as the source of boron. The size of precursor nanoparticle was controlled using the pH parameter inside the sol, and the formation of primary nuclei of ZrB2 phase and their crystallized amount were investigated using the temperature parameter. To evaluate the mechanism of product formation during the sol-gel process, TEM, SEM, DTA/TG, RAMAN, XRD, FTIR, and DLS methods were used. DLS analysis showed that the size of precursor particle inside the sol at pH less than 5 was below 10 nm. Measurements of viscosity and zeta potential inside the sol showed that in the acidic range, the particle stability decreases with increasing pH. Mixing of precursor particles at molecular level inside the sol was one of the important reasons in reducing the synthesis temperature of ZrB2 particles. FTIR analysis on chemical bonds showed that Zr-O-B bond was formed inside the gel powder. DTA analysis showed that the primary nuclei of ZrB2 particles were formed at a temperature of about 1400 °C. XRD observations proved that the primary nuclei of the ZrB2 phase crystallized and grew at a temperature of about 1500 °C. Surface research revealed that the specific surface area of the synthesized ZrB2 particles is equivalent to 115 m2/g, and also the surfaces of these particles are porous, and the size of these porosities is in meso range. SEM analysis showed that the particle size of ZrB2 having homogeneous morphology is about 50 nm. TEM microstructural analysis revealed that ZrB2 particles were formed uniformly and orderly in very fine dimensions. Highlights: Synthesis of controlled ZrB2 nanoparticle through pH-assisted sol-gel is presented. The most important goal is to achieve very high homogeneity with the appropriate chemical composition of the product. The results showed exceptional role of pH, temperature and ratio of precursors on final product characteristics. [ABSTRACT FROM AUTHOR]

Cubic specimens from AISI 316 stainless steel were multiaxially forged to 15 passes and annealed at 1200 °C for 1, 2, and 3 h and finally sensitized at 700 °C for 24 h. Examination of samples indicated that the hardness of the annealed samples was reduced from 153 to 110, 81, and 74 HV for as-received sample and under 1, 2, and 3 h of annealing, and increased from 245 to 288 HV for samples forged at 3 and 7 passes. However, no significant changes were observed in a large number of passes and at about 300 HV. Degree of sensitization of samples was increased to approximately 27.3% at 3-h annealing but reduced to 1.23% by 15 passes of MF. The potentiodynamic polarization test shows that the breakdown potentials decreased with annealing time from 0.6 to − 102 (mV/SCE) for as-received and 3-h annealed specimen. These potentials increased to approximately − 16.5 mV with the increase in MF passes to 15. These observations indicated that the chromium carbide deposition affects Cr-depleted zone, which can subsequently affect the degree of sensitization and pitting corrosion resistance of AISI 316 austenitic stainless steel. [ABSTRACT FROM AUTHOR]