Toughening mechanism for Ni–Cr–B–Si–C laser deposited coatings

Abstract

Laser deposited coatings were made from Colmonoy 69 Ni-Cr-B-Si-C alloy and Nb-modified Colmonoy 69 using laser cladding with powder injection. Addition of Nb was done to decrease the structural scale of Cr boride precipitates by providing Nb-rich nucleation agents. The purpose of the study was to evaluate the viability of microstructural refinement as a toughening mechanism for Ni-Cr-B-Si-C alloys. The results show that although a significant refinement of the Cr-rich precipitates while preserving the original level of hardness could be induced in these alloys by a suitable addition of Nb, cracking susceptibility of the deposits was not decreased. This is attributed to the continuous network of hard eutectics providing an easy route for crack growth. The outcome of this work points out that an effective toughening mechanism for Ni-Cr-B-Si-C alloys should include not only refinement of the hard precipitates, but also modification of the eutectic structure.

In-situ synthesized Ni–Zr intermetallic/ceramic reinforced composite coatings on zirconium substrate by high power diode laser

“…The value of dilution ratio of the coating was calculated as nearly 50%, so the transition zirconium element diffusing in the molten pool reacted with other alloying elements and it can be predicted that a large number of Zr-containing compounds were formed Previous works by I. Hemmati [20,29] shown that hardfacing Ni-Cr-B-Si alloy had a tendency to form multiple microstructures. In this study, the same coating exhibits various microstructures along the depth of the deposit.…”

“…One of reasons for such tendency discussed in Ref. [20] was that Ni-Cr-B-Si alloy had a large solidification range, and it is possible to follow a variety of solidification paths at different cooling rates. Moreover, the melting of some zirconium substrate near the interface and the effect of Marangoni movement [30,31] both resulted in the nonuniform distribution of elements in the molten pool.…”

“…In addition, the decomposition of WC added into powders at high temperature could not be neglected [19]. Hemmati et al [20,21] evaluated the viability of microstructural refinement as a toughening mechanism of Ni-Cr-B-Si-C coatings and pointed that both the hard precipitations and modification of the eutectic structures could improve toughness. Some transition metal elements (especially Zr, Nb) satisfied the rules proposed by Hemmati et al [20] for selecting refining elements suitable for Ni-Cr-B-Si coatings.…”

“…Hemmati et al [20,21] evaluated the viability of microstructural refinement as a toughening mechanism of Ni-Cr-B-Si-C coatings and pointed that both the hard precipitations and modification of the eutectic structures could improve toughness. Some transition metal elements (especially Zr, Nb) satisfied the rules proposed by Hemmati et al [20] for selecting refining elements suitable for Ni-Cr-B-Si coatings. So the melting of transition metal substrate could not be ignored when cladding Ni-Cr-B-Si coatings on the surface of zirconium alloys.…”

Preparation, microstructural evolution and properties of Ni–Zr intermetallic/Zr–Si ceramic reinforced composite coatings on zirconium alloy by laser cladding

“…In consideration of Ni-Zr intermetallic compounds and Zr-Si ceramics exhibiting higher hardness than most zirconium alloys and that Ni-Cr-B-Si alloy is a kind of conventional cladding powder [43], Ni-Cr-B-Si alloying powder was selected to be laser cladded on zirconium alloy. The aim of present work is to in situ synthesize Ni-Zr intermetallics/Zr-Si ceramics reinforced composite coatings on zirconium alloy by high power diode laser, reveal phase constituents and microstructural evolution and evaluate the wear resistance of coatings.…”