In-situ precipitation of TiC upon PTA hardfacing with grey cast iron and titanium for enhanced wear resistance

doi:10.1016/j.surfcoat.2012.11.003

Surface and Coatings Technology

Volume 214, 15 January 2013, Pages 63-68

https://doi.org/10.1016/j.surfcoat.2012.11.003 Get rights and content

Abstract

Titanium and grey cast iron powders were blended and deposited by plasma transferred arc onto mild steel substrates. The powders were injected directly into the arc by a stream of inert gas. The grey cast iron provided the iron matrix and the excess carbon content for reaction and precipitation of titanium carbides. The microstructure of the overlay was analysed by optical microscopy and scanning electron microscopy, and the respective phases were identified by X-ray diffraction. Microhardness measurements were taken from representative areas and the wear behaviour was assessed under low-stress abrasion conditions. The results show that the addition of titanium produced a significant change in the microstructure of the overlays, increased surface hardness and enhanced wear resistance compared to overlays produced without titanium.

Highlights

► A composite material was produced in-situ using a PTA system. ► The blend of grey cast iron and titanium powders produced Fe–TiC composite overlays. ► The composite overlays exhibited high hardness and high wear resistance. ► The microstructure and the present phases were analysed. ► The opportunities and limitations of this material/processing route are discussed.

Introduction

Metal matrix composite (MMC) materials combine the high strength and high elastic modulus of ceramic phases with the toughness and ductility of the metallic matrix [1]. Such a unique combination of mechanical properties makes MMCs very attractive for a large number of applications.

MMCs have been traditionally produced by adding ceramic phases in the solid state, to a molten metal (casting) or to a bed of metallic powder (powder metallurgy). As a consequence of their differing densities and low wettability in molten metals, ceramic particles are difficult to add and can be unevenly distributed. Moreover contamination of reinforcing particles may cause poor bonding with the metallic matrix [2]. One way to overcome these issues is to produce the ceramic phase in-situ [3].

Reinforcing phases can be synthesised in-situ by chemical reactions between alloying elements during fabrication [1], e.g. carbon and titanium or another carbide forming element. The benefits of this approach include: thermodynamic stability of the reinforcing phase, clean interfaces and better bonding between the ceramic and metallic phases, as well as finer size and better distribution of the ceramic particles. Moreover, the synthesis of MMCs during direct metal deposition has received increasing attention in recent years.

Direct metal deposition techniques, such as plasma transferred arc welding or laser cladding, permit coating of specific areas of a substrate. The former technique, i.e. PTA, offers additional benefits associated with its lower cost and wider availability in industry. Both techniques have been extensively used to apply wear resistant MMC surface layers using blends of metallic and ceramic powders. More recently, several authors have explored the fabrication of MMCs in-situ, with particular emphasis on Ni–Ti–C alloys applied by laser cladding [4], [5], [6], [7]. In most cases, a blend of metallic powders and graphite is placed on the substrate and a laser beam is used to melt them and produce the composite overlay. Although effective, this approach imposes limitations in the thickness of the overlay and the geometry of the substrate.

Recent attempts have also been directed at feeding the powders in a stream of inert gas with some success [8]. Although this method can produce thicker overlays, the injection of low density powders, such as graphite, offers technical difficulties related to high gas pressures and complex fluid dynamics developed during deposition, particularly when electric arcs are used as a source of heat [9].

In this project, the carbon content needed for in-situ synthesis of the MMC was introduced in solution with the iron matrix. A blend of grey cast iron and titanium powders was used to synthesise Fe–TiC composite overlays in-situ by plasma transferred arc. The microstructure and the wear resistance of such composite overlays were studied and the opportunities and limitations of this approach are discussed.

Section snippets

Materials and methods

The specimens were cut from a bright mild steel bar into slabs that are 100 mm in length, 32 mm in width and 10 mm in thickness. All samples were ground with #120 emery paper to remove any traces of oxide scale and subsequently degreased with acetone. Finally, the samples were pre-heated to 150 °C prior to the deposition of the overlays to eliminate adsorbed moisture.

The material used for the overlays was a mixture of 88 wt.% grey cast iron (Fe3.5C3SiMn alloy) and 12 wt.% commercially pure titanium

Microstructure

The typical macroscopic appearance of the overlays deposited on the mild steel slabs is illustrated in Fig. 2. Both GCI and GCI + Ti overlays exhibited a good appearance, free of porosity and cracks, and with an effective overlay thickness of approximately 4 mm. Some differences were observed in the surface roughness and in the bead pattern of the overlays, which could be attributed to the castability characteristics of each alloy.

Observations conducted with an optical microscope on both alloys

Discussion

In the previous section, the worn surfaces of the GCI + Ti specimens were described. From these observations, the higher wear resistance is mainly attributed to the presence of TiC precipitates, while the higher hardness of the martensitic matrix is believed to produce a second-order contribution. Therefore, the possibility to manipulate the microstructure, particularly the volume fraction and distribution of TiC precipitates, is of interest.

The volume fraction of TiC observed in the

Conclusions

From the experimental observations and analyses presented previously, it is concluded that:

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It is possible to synthesise Fe–TiC composite overlays in-situ by plasma transferred arc from a blend of grey cast iron and titanium powders.
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The addition of Ti to grey cast iron results in microstructures consisting of an even distribution of fine TiC precipitates in a martensitic matrix.
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The composite Fe–TiC overlays produced in this way show increased microhardness and high wear resistance under

References (17)

S.C. Tjong et al.
Mater. Sci. Eng. R
(2000)
Y. Wang et al.
Mater. Des.
(1999)
S. Yang et al.
Mater. Sci. Eng. A
(2003)
Y. Li et al.
Mater. Des.
(2009)
C. Cui et al.
J. Mater. Process. Technol.
(2007)
S. Gopagoni et al.
J. Alloys Compd.
(2011)
X.H. Wang et al.
Surf. Coat. Technol.
(2006)
Z. Kamdi et al.
Wear
(2011)

There are more references available in the full text version of this article.

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In-situ precipitation of TiC upon PTA hardfacing with grey cast iron and titanium for enhanced wear resistance

Abstract

Highlights

Introduction

Section snippets

Materials and methods

Microstructure

Discussion

Conclusions

Mater. Sci. Eng. R

Mater. Des.

Mater. Sci. Eng. A

Mater. Des.

J. Mater. Process. Technol.

J. Alloys Compd.

Surf. Coat. Technol.

Wear