D. Tsipas

Boriding of nickel in a fluidized bed reactor

Abstract Heat treatments of alloys in fluidized bed reactors have been carried out for more than 25 years. Recently, this technology has been used for surface engineering applications in the deposition of hard and/or corrosion resistant layers. In the present paper we used FBT to deposit boride coatings on nickel metal. The coatings were examined by means of optical microscopy, X-rays diffraction and Vickers microhardness in terms of the coating’s morphology, thickness, hardness and phase formation. The coating’s tribological properties were evaluated under dry wear. The as-produced coatings are characterized by good uniformity and it was found that only Ni 3 B (space group Pnma ) was formed during the treatment. Furthermore, the boride layer improved the tribological properties of nickel.

Deposition of hard and/or corrosion resistant, single and multielement coatings on ferrous and nonferrous alloys in a fluidized bed reactor

Abstract Heat treatments of alloys in fluidized bed reactors have been carried out for more than 25 years. Recently, this technology has been used for surface engineering applications in the deposition of hard and/or corrosion resistant layers. In the present paper we used fluidized bed technology (FBT) to deposit hard boride coatings on steel and titanium alloys and multielement Cr–Al–Hf and Yt coatings on steel alloys. The coatings were characterized using optical microscopy, electron microscopy and X-ray diffraction (XRD). The coatings porosity thickness and microhardness were evaluated as a function of processing parameters.

A comparative study of boride coatings obtained by pack cementation method and by fluidized bed technology

Abstract Pack cementation is a surface treatment method which has been used, during the last 50 years, for the deposition of a wide range of coatings, among them borides, onto steel substrates. Recently, a new method for the deposition of hard and/or corrosion-resistant coatings, the fluidized bed technology, has been developed. In this paper, a comparative study of the boride coatings on low-carbon steel, which were obtained both by fluidized bed and pack cementation methods, was carried out. In both cases, the produced coatings are characterized by very good adherence and it was found that only one phase belonging to Fe2B was formed during the treatments. The pack cementation procedure resulted in coatings with residual stresses and preferred orientation, while the fluidized bed borides are characterized by strain-free grains with random distribution.

Boron-aluminide coatings applied by pack cementation method on low-alloy steels

Abstract A simultaneous one-step boroaluminizing process has been performed on a 2.25Cr–Mo steel by means of pack cementation method using a B/Al boriding powder. Three distinct regions were found in the coatings consisting of an outer Al-rich layer, a transition region containing Al and Fe and an inner layer containing mostly B and Fe. The layers were characterized by means of optical and scanning electron microscopy (SEM) in terms of coatings morphology and thickness. X-ray diffraction (XRD) was used in order to detect the phases formed and the presence of iron aluminide and boride phases in the coating due to the boroaluminizing process.

Surface treatments in fluidized bed reactors

Heat treatments of alloys in fluidized bed reactors have been carried out for more than twentyfive years. More recently this technology has been used for carrying out nitriding, carburizing and similar surface treatments. This technology offers certain advantages over other traditional methods for Surface Engineering. These advantages include a more precise process control, greater flexibility and more efficient mass and heat transfer control during the process. In this paper we present a design of a fluidized bed reactor capable for carrying out single, and multilayer surface coatings.

Boride coatings on non-ferrous materials in a fluidized bed reactor and their properties

Abstract Fluidized bed technology has been successfully used in the formation of different types of coatings, e.g. aluminizing [Surf. Coat. Technol. 120 (1999) 151; Steel Res. 66 (1995) 318; J. Mater. Sci. 35 (2000) 5493], chromizing [Surf. Coat. Technol. 120 (1999) 151; Steel Res. 66 (1995) 318; J. Mater. Sci. 35 (2000) 5493], nitriding [Heat treatment in fluidized bed furnaces, 1993], carburizing [Heat treatment in fluidized bed furnaces, 1993], carbonitriding [Heat treatment in fluidized bed furnaces, 1993]. Recently, this technology has been used for the deposition of hard boride layers onto ferrous substrates [Mater. Lett. 51 (2001) 156; Fifth International Conference on Heat Treatment Materials, Budapest, Hungary, vol. 3, 1986]. In the present paper, we used fluidized bed technology to deposit boride coatings onto non-ferrous metals and alloys. The coatings were examined by means of optical microscopy, Vickers microhardness and X-ray diffraction, to determine thickness and morphology, phase formation and properties. The properties of dry wear and thermal cycling oxidation of the coatings were evaluated. The as-produced coatings were characterized by adequate thickness and improved wear and oxidation resistance.

Boro-nitriding of steel US 37-1

In this paper, we present a novel duplex surface treatment carried out on steel US 37-1. The as-produced multi-layer coating was characterised by optical microscopy, SEM, EDX and X-ray diffraction (XRD) and exhibited excellent adherence and morphology. The resulting layers were mainly borides, nitrides and boronitrides.

Boriding of titanium alloys in a fluidized bed reactor

Fluidized bed technology has been successfully used in the formation of different types of coatings e.g. aluminizing [1–3], chromizing [1–3], nitriding [4], carburizing [4], carbonitriding [4]. Limited information however exists on boride coatings obtained using fluidized bed technology, though the method is simple, efficient and environmentally friendly. Boride coatings on steel have been reported to have an excellent combination of properties [5, 6, 10], and titanium borides are well known for their high hardness and excellent corrosion and wear resistance. However, no reference could be cited in the literature concerning Tiboride coatings, on Ti alloys obtained in a fluidized bed reactor. Ti and its alloys, especially with Al, are attracting considerable attention because of their potential use as low-density and high temperature structural materials [14–16]. Their inadequate oxidation resistance at elevated temperatures (>800 ◦C) however limits their practical applications. Addition of alloying elements such as Nb, Si, C, B do improve the oxidation resistance of these alloys, but the amounts of these additives should be controlled at low levels [11]. Use of surface modification techniques such as ion implantation of Al ions in to Ti-Al alloys, produce a high oxidation resistant TiAl3 coating, whose final overall oxidation resistance is nevertheless mitigated by the inherently developed cracks and voids in the coating [12, 13]. On the other hand, thermochemical diffusion processing such as boronizing in fluidized beds is a promising method for improving the oxidation resistance of Ti and its alloys, as it is a flexible and low cost method, yielding boride layers of excellent quality and uniformity. The main advantage of the process of fluidization, is the high rate of mass and heat transfer, which results in a uniform temperature throughout the volume of the reactor and a flash mix of all compounds contained in it, thus yielding high quality coatings [7–9]. Additional advantages arise from, the process capability for quick parameter adjustment, the relatively low capital and operation costs and its being environmentally friendly. Some of the main parameters affecting the quality of the fluidization process and that of the produced coatings, obviously are the properties of solids and fluids used, bed geometry, gas flow rate, type of gas distributor and overall reactor design. This paper presents some of the results produced by a study of boride coatings applied onto Ti-Al-V alloys by the fluidized bed process. The fluidized bed reactor system used for the above and shown schematically in Fig. 1, consisted of the following five main components:

Boriding in a fluidized bed reactor

AbstractHeat treatments of alloys in fluidized bed reactors have been carried out for more than 25 years. Recently, thistechnology has been used for surface engineering applications in the deposition of hard andror corrosion-resistant layers. Inthe present paper, we used fluidized bed technology FBT to deposit boride coatings. The coatings were examined by meansŽ.of optical microscopy, Vickers microhardness and X-ray diffraction XRD in terms of coatings thickness and morphology,Ž.phase formation and properties. The as-produced coatings are characterized by very good adherence due to its tooth-shapemorphology and it was found that only one phase belonging to Fe B space group IŽ.rmcm, a s5.110 A, ˚˚ c 4.249 A was 24 formed during the treatment. q2001 Elsevier Science B.V. All rights reserved. Keywords: Boriding; Fluidized bed coatings 1. IntroductionFluidized bed technology has been successfullyused for the formation of different types of coatings,e.g. aluminizing 1–4 , chromizing 1–3 , nitridingwx wxw x wx wx5–7 , carburizing 7 , carbonitriding 7 . On theother hand, very limited information exists on boridecoatings obtained using fluidized bed technology,although the method is simple, efficient, environ-mentally friendly and the boride coatings have beenreported to have an excellent combination of proper-ties 8,9,13 . The theory of fluidization is describedwxin great detail elsewhere 10–12 . Briefly, fluidiza-wxtion is a process in which a bed of particles, e.g.Al O , behave like a liquid when a carrier gas is fed

Corrosion behaviour of boronized low carbon steel

Abstract In this paper we present the results of corrosion resistance of boronized 1020 steel in naphthenic acid and during high temperature oxidation. The boride layer, consisting of FeB in the outer region and Fe 2 B in the inner zone, was found to be extremely resistant to naphthenic acid containing media, both in the liquid and vapour phase. During high temperature oxidation in air at 650°C a very thin, 10 M protective oxide layer was formed on the boronized steel, indicating that the boride layer acts as a barrier to oxygen and/or Fe diffusion. Finally both the morphology and distribution of FeB/Fe 2 B layers changed during high temperature oxidation.