Dry wear behaviour and its relation to microstructure of novel 6092 aluminium alloy–Ni3Al powder metallurgy composite
Introduction
Interest in the tribological properties of aluminium alloys has increased substantially over recent years because of the potential for weight savings in many applications. Much attention has been focused on aluminium-based metal matrix composites (MMCs) [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37]. The wear resistance of Al-based MMCs has been found to be superior to the corresponding monolith in many studies (e.g. [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17]). However, many authors have observed a critical load above which the composite wears at an equal, and sometimes substantially greater, rate than the monolith (e.g. [11], [14], [15], [37]). The transition in wear rate observed for many MMCs is speed and test temperature dependent, and is generally believed to be a result of fibre fracture [14], [15] and voiding/cracking between reinforcement and the matrix [7], [14], [15], both of which lead to fragmentation and delamination of the surface. Thus, the maximum load a composite can support during sliding without excessive wear is, in part, determined by the fracture toughness of the reinforcement, although the extent of fracture is also a strong function of reinforcement size and shape [14], [15], [19], [20], [21], [22], [23].
An additional drawback of Al-based MMCs with reinforcing phases, such as SiC and Al2O3, is the tendency of the reinforcement to act as a second-body abrasive against the counterface, increasing counterface wear rates (e.g. [38]). In addition, reinforcement liberated as wear debris acts as a third-body abrasive to both surfaces. The two effects can result in a higher wear rate for the system as a whole when an MMC is used as one component compared with the monolith. While the extent of this problem depends on the mechanical properties of the counterface, it has undoubtedly restricted the use of these materials in several potential applications.
Al-based MMCs reinforced with intermetallics were first proposed by Yamadi and Unakoshi [39], while Omura et al. [32] first demonstrated that an Al alloy casting containing 5 vol.% Ni3Al achieved the same wear resistance as a die cast conventional Al-MMC. Later, Ruutopold et al. [40] suggested that Ni3Al would be an optimum intermetallic reinforcement, but observed extensive reaction between the intermetallic and the matrix when composites were produced via the casting route. González-Carrasco et al. [41] demonstrated that such reactions could be largely avoided by fabricating the composite via the powder metallurgy route, although subsequent heat treatment led to reaction between matrix and reinforcement [42]. The same group subsequently showed [24] that the presence of 5 vol.% Ni3Al enhanced the wear resistance of pure aluminium, and that for particles of size 100–125 μm, the intermetallic acted as a load-bearing reinforcement.
Following on from the work of Lieblich and co-workers [24], [41], [42], this paper reports the wear behaviour of Al–Mg–Si/15 vol.% Ni3Al composite produced by the powder metallurgical route. The Ni3Al, with a hardness intermediate between the matrix and conventional reinforcements such as SiC, was produced by self-propagating high temperature synthesis (SHS), a cheaper production route than gas atomisation used in the earlier work [24], [41], [42]. In addition, simplified blending, cold pressing and extrusion procedures were also used to reduce the overall production costs, the full details of which will be published elsewhere. The composite is compared to a monolith comprising the matrix of the composite and produced by the same process conditions. The wear characteristics as a function of load are reported with particular attention paid to the interaction between the Al samples and the ferrous counterface.
Section snippets
Experimental
Monolith and composite samples were produced by a powder metallurgy route. The 6092 aluminium alloy powder, with mean particle size (d50) of 26 μm and composition given in Table 1, was produced by inert gas (argon) atomisation and supplied by Alpoco, Sutton Coldfield, UK. Intermetallic Ni3Al powder, supplied by INASMET, San Sebastian, Spain, was obtained by self-propagating SHS. In this process, powders of Ni (∼5 μm) and Al (∼100 μm) were mixed in the appropriate proportions, along with a small
Results
Fig. 2a gives an optical micrograph of the as-extruded 6092 Al alloy–15 vol.% Ni3Al composite, showing a homogeneous distribution of the intermetallic. A mean Ni3Al particle size of 6.5 μm was measured, although a small fraction of particles were found up to ∼40 μm diameter. The good bond between the intermetallic and matrix was demonstrated by the absence of decohesion on tensile fracture surfaces (to be reported elsewhere). Detailed TEM and SEM confirmed the absence of cracking or reaction at
Discussion
The wear surface observations (Fig. 6) suggest that the wear mechanism at 42 N was mild/oxidational wear for the composite, but adhesive/oxidational for the monolith (as shown by the extensive oxide on the surface of the composite, Fig. 7c, that was generally absent on the monolith, Fig. 7a). In the present case, oxidational wear was a more complex process than that suggested by the classical oxidational wear papers [45], and resulted in the formation and detachment of an MML (giving the fine
Conclusions
- 1.
The wear performance of a novel Al alloy–Ni3Al composite is reported, produced by a cost-effective powder metallurgical route.
- 2.
At low loads of 42 and 91 N, a 6092 Al Alloy–15 vol.% Ni3Al composite offered superior wear resistance compared to a 6092 monolith. In contrast, the monolith showed superior wear resistance to the composite at the highest load, 140 N.
- 3.
At all loads, wear of the monolith lead to a grooved surface and sheet-like wear debris, consistent with rachetting wear. In addition, a
Acknowledgements
Financial support from the European Community (project number: BE 97-4455) is gratefully acknowledged. Supply of Ni3Al by INASMET, San Sebastian, Spain, and the 6092 Al alloy powder by Alpoco, Sutton Coldfield, UK, is also gratefully acknowledged. Similarly, the authors are grateful to Creuzet, Marmande, France, for undertaking the extrusions.
References (50)
- et al.
Wear
(1982) - et al.
Wear
(1992) - et al.
Mater. Sci. Eng. A
(1993) - et al.
Tribol. Int.
(1994) - et al.
Wear
(1995) - et al.
Wear
(1995) - et al.
Scripta Met. Mater.
(1990) - et al.
Wear
(1992) - et al.
Wear
(1992) - et al.
Acta Mater.
(1996)
Acta Mater.
Wear
Mater. Sci. Eng. A
Mater. Sci. Eng. A
Wear
Wear
Mater. Sci. Eng.
Intermetallics
Wear
Tribol. Int.
Wear
Wear
Wear
J. Mater. Sci.
Mater. Sci. Technol.
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