Repair of Erosion Defects in Gun Barrels by Direct Laser Deposition
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Steffen Nowotny, Joerg Spatzier, Frank Kubisch, Siegfried Scharek, Jens Ortner, and Eckhard Beyer (Submitted December 20, 2011; in revised form July 23, 2012) In recent years the development of functional carbide coatings follows the trend to use composite powders with fine grained hard particles. In addition to thermal spraying, laser cladding is a suitable surface technology in particular for dynamically loaded components, and it is widely used for the manufacturing of coatings as well as complex 3D structures. The paper presents an application addressing the repair of erosion defects in large gun barrels using a novel internal diameter laser cladding head. The most promising material systems are TiC- and VC-based metal-matrix composites. Samples were evaluated in a special erosion test that emulates realistic load conditions. In this test, the materials are exposed to extreme stresses by temperature and pressure shocks, a very reactive atmosphere and erosive particles. As result, TiC-based coatings showed the best performance, and they are applicable for both repair and surface protection of inner surfaces of components and tools.
Keywords
composites, direct metal deposition, gun barrel, internal diameter cladding, laser processing, surface modification, repair
The two objectives of the work presented here were, first, to develop a coating method for repairing the erosion damage applying near net shape material depositions and, second, to develop a coating material, which is resistant enough to endure the harsh conditions in large caliber gun barrels.
1. Introduction Inner surface depositions for heavily stressed large tubular components and tools are challenging applications for thermal coating technologies. Examples include concrete extruder tubes in the heavy construction industry, extruder tubes used in the plastics manufacturing industry, oil drilling equipment, or even large gun barrels. Those large caliber gun barrels >100 mm are extremely stressed. The maximum temperature of propellant core flow gases is about 3300 K and the combustion gases which are in contact with the walls reach 1600 K. The peak pressure ranges between 300 and 400 MPa, causing a mechanical expansion of up to 1%. The hot and highly reactive gas flow accelerates the projectile to about 1500 m/s. In spite of a 350-lm thick hard chrome plating, the combination of these harsh conditions leads to erosive wear. However, the lifetime of large gun barrels is not limited by fatigue failure, but by erosive defects, which are typically up to 40 mm long, 5-10 mm wide and 1-3 mm deep. Because these parts are very expensive, the repair of local defects would be highly profitable.
Steffen Nowotny, Joerg Spatzier, Frank Kubisch, Siegfried Scharek and Eckhard Beyer, Fraunhofer Institute Material and Beam Technology IWS, Dresden, Germany; Jens Ortner, Wehrwissenschaftliches Institut fu¨r Werk- und Betriebsstoffe WIWeB, Erding, Germany; and Eckhard Beyer, University of Technology, Dresden, Germany. Contact e-mail: Steffen. [email protected].
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