A. H. Dent

University of Nottingham, Nottingham, ENG, United Kingdom

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Publications (3)5.53 Total impact

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    ABSTRACT: High velocity oxy-fuel (HVOF) thermal spraying was used to deposit coatings, approximately 200 μm thick, of a commercially available Ni-Cr based alloy containing boron and carbon [Ni-23.5Cr-3.8Cu-0.8Fe-5.9Mo-3.4W-2.8B-4.3C (at.%)]. Powder and coating microstructures were investigated by a combination of X-ray diffraction, scanning electron and transmission electron microscopy. The coatings had layered morphologies due to the deposition and solidification of successive molten or semi-molten splats. The splat microstructures consisted of a Ni-rich metallic matrix containing a small fraction of M23C6 particles ∼50 nm in size. The Ni-rich matrix had a predominantly crystalline structure with only a small fraction of amorphous phase regions. Cr2O3 and NiCr2O4 oxide phases occurred in the form of either intersplat lamellae or globules, with Cr2O3 being the predominant oxide. Coating microhardness values were found to be ∼6.0 GPa which is significantly higher than that of B- and C-free nickel-based alloys similarly deposited.
    Surface and Coatings Technology 01/2001; · 1.94 Impact Factor
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    ABSTRACT: High velocity oxy-fuel (HVOF) thermal spraying was used to deposit Ni–Cr–Mo–B alloy coatings, approximately 200 μm thick, onto mild steel substrates. Gas atomised powders of three different compositions were used in the experiments. Powder and coating microstructures were investigated by a combination of X-ray diffraction, scanning electron and transmission electron microscopy and differential thermal analysis (DTA). The coatings had layered morphologies due to the deposition and solidification of successive molten or semi-molten splats. The splat microstructures consisted of a Ni-rich metallic matrix containing a small fraction of M3B2 particles 10–30 nm in size and with a tetragonal crystal structure. The Ni-rich matrix comprised both crystalline and amorphous regions. The former was predominantly nanocrystalline with a grain size of ca. 50 nm and DTA showed that the crystallization temperature of the amorphous phase varied from 800 to 860 K depending on the alloy constitution. Cr2O3 and NiCr2O4 oxide phases occurred in the form of either intersplat lamellae or globules. The thin lamellar oxides exhibited the α-Cr2O3 crystal structure whereas globular oxides, up to 1 μm in size, were found with both α-Cr2O3 and NiCr2O4 structures.
    Materials Science and Engineering A 01/2000; 283:242-250. · 2.11 Impact Factor
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    ABSTRACT: The corrosion characteristics of two Ni-Cr-Mo-B alloy powders sprayed by the high-velocity oxy-fuel (HVOF) process have been studied using potentiodynamic and potentiostatic corrosion analysis in 0.5 M H2SO4. The deposits were also microstructurally characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM) (utilizing both secondary electron and backscattered electron modes), and transmission electron microscopy (TEM). Results from the microstructural examination of the two alloys have revealed a predominantly amorphous/nanocrystalline face centered cubic (fcc) matrix containing submicron boride precipitates as well as regions of martensitically transformed laths. Apparent recrystallization of the amorphous matrix has also been observed in the form of cellular crystals with a fcc structure. The oxide stringers observed at splat boundaries were found to be columnar grained α-Cr2O3, though regions of the spinel oxide NiCr2O4 with a globular morphology were also observed. The coatings of the two alloys exhibited comparable resistance to corrosion in 0.5 M H2SO4, as revealed by potentiodynamic tests. They both had rest potentials approximately equal to −300 mV saturated calomel electrode (SCE) and passive region current densities of ∼1 mA/cm2. Microstructural examination of samples tested potentiostatically revealed the prevalence of degradation at splat boundaries, especially those where significant oxidation of the deposit occurred.
    Journal of Thermal Spray Technology 08/1999; 8(3):399-404. · 1.48 Impact Factor