Nickel-based superalloy Nimonic 80A was pack-borided in a solid medium at temperatures of 850 °C and 950 °C for 2 h and 4 h using silicon-free boriding powders. To investigate the effects of the boriding treatments on mechanical properties (hardness, modulus of elasticity, fracture toughness) and high temperature oxidation resistance, the layers grown on the surfaces were characterized using optical and scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffractometry, and evaluated using microhardness, nanoindentation, wear and oxidation tests. Wear tests were performed on untreated and borided Nimonic 80A alloys using a ball-on-disc tribometer at room temperature and at 500 °C under dry sliding conditions. Oxidation tests were carried out in air at 1000 °C for 5 h, 25 h and 75 h. Characterization studies revealed a smooth, 22 to 86 μm thick crack-free boride layer consisting mainly of Ni2B and minor quantities of CrB, Cr2B and Cr5B3 in the borided samples. The hardness and elastic modulus of the boride layer was measured as 15.57–18.95 GPa and 142–217 GPa, respectively. Increasing the boriding temperature and time increased the concentrations of chromium in the boride layer. The hardness and elastic modulus of the boride layer increased with chromium content while its fracture toughness decreased. The boriding treatments improved the dry sliding wear resistance. Increasing boriding time and temperature generally led to a higher wear resistance values. However, the treatments had no significant effect on oxidation resistance. The results of this study show that boriding can significantly improve the wear resistance of Nimonic 80A without compromising its oxidation resistance.

Characteristics, high temperature wear and oxidation behavior of boride layer grown on nimonic 80A Ni-based superalloy

Low-temperature aluminizing influence on degradation of nimonic 80A surface: Microstructure, wear and high temperature oxidation behaviors

The present work aims to study the mechanical and tribological properties of titanium boride layer processed by a thermochemical boriding treatment, which was carried out in a salt bath consisting ...

Mechanical and tribological behaviour of titanium boride coatings processed by thermochemicals treatments

In this study, three different types of stainless steels, AISI 304, AISI 420, and AISI 430 were pack borided under 850 °C–925 °C–1000 °C for 2, 4, and 6 h, respectively. Morphologies of coating wer...

Investigation of mechanical, kinetic and corrosion properties of borided AISI 304, AISI 420 and AISI 430

Influence of nickel silicides presence on hardness, elastic modulus and fracture toughness of gas-borided layer produced on Nisil-alloy

Incoloy 909 superalloy was treated at 950°C to form coatings of different chemical composition by thermochemical diffusion. Packing of the samples in reactive powders lead to the formation of iron borides (Fe2B and FeB) together with nickel boride, NiB, and nickel silicide, Ni2Si, on the surface of the alloy depending on the exposure time. X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy analyses suggest that growth of the coatings is controlled by diffusion of reactive species into the metal structure. Microabrasion wear resistance of the coated specimens was studied at 1 N load for a fixed sliding speed of 0.11 m s−1 and it was compared against uncoated samples of the alloy. It was found that coating the alloy for 12 and 20 h increased the hardness of the alloy and therefore its wear resistance.

Mechanical stability of boron-based coatings grown on Incoloy 909 superalloy by thermochemical diffusion

The oxidation behaviour of Incoloy 909 superalloy subjected to diffusion boronizing treatments was studied at 750 and 850°C in atmospheres of dry air and a mixture of dry air + water vapour for tim...

Oxidation behaviour of borided Incoloy 909

The oxidation characteristics of a roll-grade high-speed steel with different tempering heat treatments were studied under thermal cycling conditions at 650 °C in laboratory dry air. The oxidation kinetics of the steel could be described by the parabolic rate law and were a function the tempering temperature. Characterization of the oxide scales was conducted by X-ray diffraction and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. It was found that the chemical composition of the oxide scales depended on the tempering temperature and favoured the formation of Fe3O4, Fe2O3, (Fe,Cr)3O4 and (Fe,Cr)2O3. Thermal cycling of the steel promoted the fracture and spallation of the oxide scales formed, causing increments in the oxidation rates. The steel also experienced a progressive reduction in its hardness with the number of thermal cycles applied, which could be also related to the thermal process. The results of this investigation are explained in terms of the microstructural evolution of the alloy due to variations in the tempering temperature.

Mauro J. Gaona-Martínez

Papers

Mechanical stability of boron-based coatings grown on Incoloy 909 superalloy by thermochemical diffusion

Oxidation behaviour of borided Incoloy 909

Effect of Tempering on the Oxidation Behaviour of a Roll-Grade High-Speed Steel During Thermal Cycling

Surface and Subsurface Defects Formed in a Cold-Rolled Electrical Steel