Processing of Carbon Nanoparticle-Enriched AISI H11 Tool Steel Powder Mixtures in DED-LB/M for the AM of Forging Tools with Tailored Properties (Part II): Influence of Nanoscale Carbon Additives on Microstructure and Mechanical Properties

Abstract

A promising approach for producing parts with outstanding properties in directed energy deposition (DED-LB/M) provides the application of tailored powder mixtures processed by applying in situ alloying strategies. In this work, DED-LB/M was used to manufacture multilayer specimens from AISI H11 steel powders enriched with carbon nanoparticles (C-np) in concentrations of 0.1 wt.-% and 0.2 wt.-%. The scientific aim was to investigate the impact of C-np on the microstructural (particularly retained austenite content (RA-c) and grain size) and mechanical properties (specifically hardness and compression yield strength) of the manufactured specimens. It was shown that the addition of C-np to the H11 powder leads to a stronger distortion of martensite as well as significantly enhancing the RA-c. Furthermore, the C-np seem to favor the formation of finer martensite, as can be verified with XRD and EBSD. Under as-built conditions, the mean hardness increases from 653 ± 10 HV1 for the H11 sample to 770 ± 14 HV1 for the sample reinforced with 0.2 wt.-% C-np. At the same time, Y0.2% rises up from 1839 ± 61 MPa to 2134 ± 68 MPa. The hardness- and strength-increasing effect of the added C-np is retained even after heat treatment, similarly to the industrial standard.

Experimental Investigations in the Processing of AISI H11 Powder Blends Enriched with Tungsten Carbide Nanoparticles for the Additive Manufacturing of Tailored Hot Working Tools in the Directed Energy Deposition (DED-LB/M)—Impact of Tungsten Carbide Nanoparticles on Microstructural and Mechanical Characteristics

“…Figure 3 illustrates the experimental procedure used for the layer-by-layer manufacturing of cubic samples consisting of multiple weld track layers. A comprehensive description of the procedure for the Additive Manufacturing of multilayer test specimens can be found in [44]. In a first step, individual weld tracks were deposited on the AISI H11 substrates using different sets of process parameters.…”

“…scription of the procedure for the Additive Manufacturing of multilayer test specimens can be found in [44]. In a first step, individual weld tracks were deposited on the AISI H11 substrates using different sets of process parameters.…”

“…Table 3 gives an overview of process parameter combinations investigated. At this point, it has to be mentioned that the investigated process parameter combinations are also applicable for producing multilayer specimens with promising characteristics from AISI H11 powder mixtures modified through the addition of carbon nanoparticles; see [44]. Figure 4 shows a sketch of the bidirectional deposition strategy applied for the AM process of multi-layered builds.…”

“…At this stage, it should be noted that all combinations of process parameters are applicable to the production of almost fully dense multilayer specimens made from both unmodified AISI H11 powder and AISI H11 powder blends enriched with carbon black nanoparticles [18,44].…”

“…For the preparation of WC-np AISI H11 powder blends, a multi-stage dry-coating approach was used. The dry-coating process was already developed and successfully evaluated in a previous study in which the processing of carbon black nanoparticles reinforcing AISI H11 powder mixtures was fundamentally proven [33,44]. Subsequently, the sub-processes involved in the dry-coating procedure are listed in bullet points.…”