Recent Developments in Laser Surface Treatment
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RECENT DEVELOPMENTS IN LASER SURFACE TREATMENT B.L. MORDIKE AND H.W. BERGMANN Institut fUr Werkstoffkunde und Werkstofftechnik, Technische Universit~t, Agricolastr. 2, 3392 Clausthal-Zejlerfeld, FRG ABSTRACT Some unrelated examples are given where progress has been made in laser surface treatment in the last few years. These are large scale transformation hardening, reproducible surface melting of cast iron, surface alloying with a reaction with the surrounding atmosphere, fundamental studies of solidification and evaporation cleaning. INTRODUCTION Developments in laser technology and in manipulating techniques as well as computer technology have resulted in systems being available for a wide range of surface treatments. The highly localized heat source enables non equilibrium conditions to be achieved. Required microstructures can be produced, enabling tailor making of components with desired surface properties. The types of surface treatment can be subdivided into the classes surface modification, solid state (eq martensitic transformation) and surface melting as shown in Table I. TABLE I:
Types of Surface Heat Treatment
Treatments without melting
Treatments with melting
Rapid homogenization
Simple melting (finer structure, supersaturation) Refinement by evaporation of impurities Surface alloying Injecting particles into surface (Alloy hard metals) Cladding (thick hard metal coatings)
Transformation hardening (Martensitic transformation)
Surface annealing
Each of the applications relies on the specific features of laser treatment ie rapid heating and homogenization and subsequent self quenching. In transformation hardening the rapid quench produces a martensitic structure in the surface which improves wear and fatigue behaviour. In other applications the desired properties are achieved by homogenization of the surface layer by producing a single phase or finely divided microstructure (eg corrosion) or by surface softening (eg increasing ductility for thread rolling) or by changing the composition of the surface or by dispersion/precipitation hardening (eg internal oxidation or nitriding). Some applications of lasers are discussed in the following with examples of where new developments have recently taken
Mat. Res. Soc. Symp. Proc. Vot. 58. c 1986 Materials Research Society
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place either in the handling enabling better reproducibility and higher quality of existing techniques or in new applications. SOLID STATE TRANSFORMATIONS Laser hardening has been used successfully to harden a variety of steels [ 1,2,3], see Table II. TABLE II: Materials and components hardened by lasers in commercial processes Component
Material
Steering Gear Housing Camshafts and Camfollowers
Ferritic malleable iron Ferritic, pearlitic and bainitic SG iron Bainitic SG iron Cast iron AISI 1050 steel AISI 1050 steel AISI 4340 steel 0.7 % C steel
Mineral Sieves Motor Blocks and Cylinders Motor Shaft Splines Cutting Blades Firing Zone Cutout Cams Electric Razor Cutter Combs
1200 'I
.1000--
800C
-
600
-
-
-
-
-
400-I
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