Microstructural Evolution During Laser Surface Alloying of Ductile Cast Iron with Titanium

Abstract

Diode laser surface alloying process was used to the in-situ synthesis of TiC-reinforced composite surface layers on the ductile cast iron substrate. The obtained composite surface layers were investigated using optical and scanning electron microscopy, and XRD diffraction.It was found that the morphology and fraction of TiC phase is directly dependent upon both the concentration of titanium in the molten pool and also the solidification rate. With increasing titanium content, the fraction of TiC increases, whereas the fraction of cementite decreases. The TiC phase promotes a heterogeneous nucleation of primary austenite grains, what reduces a tendency of cracking in the alloyed layers.

Effect of Chromium and Molybdenum Addition on the Microstructure of In Situ TiC-Reinforced Composite Surface Layers Fabricated on Ductile Cast Iron by Laser Alloying

“…During all trials, the laser spot was located on the top surface of SM, and the fast-axis of the laser beam was set parallel to the scanning direction. Based on previous work [ 23 , 24 , 25 ], the laser power and traverse speed were held constant at 1500 W and 1.25 mm/s, respectively. The powder feed rates depended on the type of the alloying material and are listed in Table 2 .…”

“…High C contents in cast iron substrates provide excellent conditions for the in situ formation of MMC surface layers via LA, with elements that tend to form carbides. Several studies on the LA of cast iron substrates have focused on the in situ synthesis of TiC-reinforced layers (TRLs) by introducing Ti into the molten pool [ 16 , 20 , 21 , 22 , 23 , 24 , 25 , 26 ]. From the point of view of the wear properties, the microstructure of the synthesized TRLs should contain a martensitic matrix with homogeneously-dispersed TiC precipitates [ 24 , 26 ].…”

“…Moreover, published data on the wear performance of Fe-based MMCs reinforced with TiC phase suggest a significant increase in the wear resistance of TRLs with increasing the TiC fraction [ 24 , 26 , 27 , 28 , 29 ]. However, reported works have shown that during the in situ synthesis of TRLs on cast iron substrates via LA, it is difficult to maintain a homogeneous dispersion of the reinforcing phase upon increasing the Ti concentration in the melt [ 23 ]. As a consequence, control over the fraction and growth morphology of the TiC particles, and also the phase composition of the matrix, is highly limited.…”

“…Previous studies [ 23 , 24 , 25 ] were undertaken to determine the feasibility of the in situ synthesis of TRLs on the DCI substrate via LA with pure Ti powder. The aim of that investigation was to establish the processing conditions that allowed the use of the entire C content in the processed substrate to optimize the TRL’s microstructure, i.e., to achieve the highest possible TiC fraction and a fully martensitic matrix.…”

Microstructure and properties of a titanium carbide reinforced coating on grey iron applied with laser cladding

“…11,12 Among them, TiC has the following advantage for cast iron: it can be readily synthesized in a laser melt pool; thus, it significantly reduces the carbon content in the matrix. [13][14][15] Janicki et al 14 found that the morphology and fraction of the TiC phase directly depends on the concentration of titanium in the melt pool and on the solidification rate. With an increased titanium content, the fraction of TiC increases, whereas the fraction of cementite decreases.…”