Hybrid cylindrical roller thrust bearing washers of type 81212 were manufactured by tailored forming. An AISI 1022M base material, featuring a sufficient strength for structural loads, was cladded with the bearing steel AISI 52100 by plasma transferred arc welding (PTA). Though AISI 52100 is generally regarded as non-weldable, it could be applied as a cladding material by adjusting PTA parameters. The cladded parts were investigated after each individual process step and subsequently tested under rolling contact load. Welding defects that could not be completely eliminated by the subsequent hot forming were characterized by means of scanning acoustic microscopy and micrographs. Below the surface, pores with a typical size of ten µm were found to a depth of about 0.45 mm. In the material transition zone and between individual weld seams, larger voids were observed. Grinding of the surface after heat treatment caused compressive residual stresses near the surface with a relatively small depth. Fatigue tests were carried out on an FE8 test rig. Eighty-two percent of the calculated rating life for conventional bearings was achieved. A high failure slope of the Weibull regression was determined. A relationship between the weld defects and the fatigue behavior is likely.
Additive manufacturing with multi-material design offers great possibilities for lightweight and function-integrated components. A process chain was developed in which hybrid steel–steel-components with high fatigue strength were produced. For this, a material combination of stainless powder material Rockit® (0.52 wt.% C, 0.9% Si, 14% Cr, 0.4% Mo, 1.8% Ni, 1.2% V, bal. Fe) cladded onto ASTM A572 mild steel by plasma arc powder deposition welding was investigated. Extensive material characterization has shown that defect-free claddings can be produced by carefully adjusting the welding process. With a tailored heat treatment strategy and machining of the semi-finished products, bearing washers for a thrust cylindrical roller bearing were produced. These washers showed a longer fatigue life than previously produced bearing washers with AISI 52100 bearing steel as cladding. It was also remarkable that the service life with the Rockit® cladding material was longer than that of conventional monolithic AISI 52100 washers. This was reached through a favourable microstructure with finely distributed vanadium and chromium carbides in a martensitic matrix as well as the presence of compressive residual stresses, which are largely retained even after testing. The potential for further enhancement of the cladding performance through Tailored Forming was investigated in compression and forging tests and was found to be limited due to low forming capacity of the material.
To improve the bond strength of hybrid components when joined by friction welding, specimens with various front end surface geometries were evaluated. Rods made of aluminum AA6082 (AlSi1MgMn/EN AW-6082) and the case-hardening steel 20MnCr5 (AISI 5120) with adapted joining surface geometries were investigated to create both a form-locked and material-bonded joint. Eight different geometries were selected and tested. Subsequently, the joined components were metallographically examined to analyze the bonding and the resulting microstructures. The mechanical properties were tested by means of tensile tests and hardness measurements. Three geometrical variants with different locking types were identified as the most promising for further processing in a forming process chain due to the observed material bond and tensile strengths above 220 MPa. The hardness tests revealed an increase in the steel’s hardness and a softening of the aluminum near the transition area. Apparent intermetallic phases in the joining zone were analyzed by scanning electron microscopy (SEM) and an accumulation of silicon in the joining zone was detected by energy-dispersive X-ray spectroscopy (EDS).
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