MATERIAL CHARACTERIZATION OF DIRECTED ENERGY DEPOSITION OF H13 TOOL STEEL AND FUNCTIONALLY GRADED H13-COPPER
Date
2022-08-30
Authors
Craig, Owen
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Abstract
The aim of this study is to determine the laser directed energy deposition (DED)
parameters for an H13-Cu functionally graded material (FGM). Monolithic steel tools
have poor thermal conductivity, reducing the cycle times. This could be improved with
the high thermal conductivity of Cu in a FGM structure. Research began with wrought
H13 heat-treated at varying tempering temperatures to examine the influence on the
microstructure and mechanical properties. DED H13 samples were produced by varying
the scanning speed and powder feed rates to examine geometrical and microstructural
influences. Several techniques were employed to characterize the materials which
included surface roughness, optical and scanning electron microscopy, hardness, X-ray
diffraction, energy dispersive X-ray spectroscopy, and scratch hardness. The top surface
roughness of the samples was found to be greater than the side surface roughness. The
addition of a draft angle to a vertical surface was shown to reduce the side surface
roughness. The deposited material undergoes rapid solidification, producing a highly
refined microstructure with near-theoretical density (99.7%). The as-printed multi-layer
samples show a cellular dendritic structure with tempered martensite and alloy carbides
in the lower layers. The top layers consist of fine lath martensite and retained austenite.
Tempering the multi-layer samples results in a homogenized microstructure of tempered
martensite and alloy carbides. There was variation in the Vickers hardness of the asprocessed samples due to the cyclic heating. Applying a heat treatment to the DEDprocessed materials reduced the hardness and variation. Scratch hardness was highest in
the as-printed condition with a heat treatment reducing the scratch resistance. No trend
was observed in the scratch response with changing the scanning speed, powder feed rate,
or number of layers. Varying H13-Cu blends were printed on wrought H13 as well as a multi-layered FGM.
Single layer and 3-layer tracks resulted in detrimental porosity and vertical cracking
characteristic of solidification cracking. The multi-layered FGM samples showed
transverse cracking and porosity. The microstructure consisted of tempered martensite,
martensite, alloy carbides, retained austenite, and a Cu-rich matrix with scattered H13
particles. There is clear separation of the H13- and Cu-rich liquids due to the miscibility
gap, aided with differential scanning calorimetry analysis. Printing onto C110 was
unsuccessful using varied laser powers resulting in inconsistent beads.
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Keywords
additive manufacturing, H13 tool steel, functionally graded materials, Copper