Blown-powder direct-energy-deposition of titanium-diboride-strengthened IN718 Ni-base superalloy

This paper reports on the adoption of TiB2 as an inoculant to fabricate IN718 via the direct energy deposition (DED) process. Effective grain refinement and low texture were achieved in IN718/TiB2 using a TiB2 powder size of d90 = 10 μm and mass fraction of 1.5 wt%. The use of low linear energy density (33.08 J/mm) produced IN718/TiB2 deposits free from large grains (>300 μm), however at the cost of the formation of interlayer defects. By comparison, the large grains were present in deposits made with a linear energy density of 78.74 J/mm and also in deposits manufactured without an included inoculant. Production of deposits at lower energies without interlayer defects was possible by reducing the powder flow rate to 7 g/min. However, this caused a moderate increase in grain size. The TiB2 inoculant reduced the Laves phase network by replacing it with homogeneously distributed Cr-, Mo-, Nb-, and B-enriched needle-shaped precipitates. Tensile strength increased by 300–500 MPa with TiB2 addition, but at the cost of significant ductility drop, regardless of the deposition conditions. The IN718 deposit displayed many micro-cracks at the network of Laves phase during tensile loading, whereas micro-cracks in the IN718/TiB2 occurred at the interface between the needle-shaped precipitates and the matrix. The strength enhancement in IN718/TiB2 was by a combination of strengthening mechanisms: grain boundary, dislocation structure formation, Orowan-type and load transfer related to the needle-shaped precipitates

The nitrocarburising response of low temperature bainite steel

The nitrocarburising response of low transformation temperature ultrafine and nanoscale bainitic steel was investigated and compared with martensite and pearlite from the same steel composition. It was found that the retained austenite content of the bainitic steel dictated the core hardness after nitrocarburising. The refined bainitic structure showed improvements in the nitriding depth and hardness of the nitrocarburised layer, compared to coarser grained martensitic and pearlitic structures, possibly due to the fine structure and the distribution of nitride forming elements

The Nitrocarburising Response of Low Temperature Bainite Steel

The nitrocarburising response of low transformation temperature ultrafine and nanoscale bainitic steel was investigated and compared with martensite and pearlite from the same steel composition. It was found that the retained austenite content of the bainitic steel dictated the core hardness after nitrocarburising. The refined bainitic structure showed improvements in the nitriding depth and hardness of the nitrocarburised layer, compared to coarser grained martensitic and pearlitic structures, possibly due to the fine structure and the distribution of nitride forming elements

Nitrocarburising and low-temperature chromising duplex surface treatment

A new duplex surface engineering process has been developed that involves the deposition of chromium on ferritic nitrocarburised steel surfaces at low temperatures. This process formed a thin and hard chromium carbonitride surface layer and is to be applied to hardened tooling used in metal forming operations for improved wear performance and die life