Effect of titanium on the boronizing behaviour of pure iron

Abstract

The effect of titanium on the boronizing behavior of pure iron with additions of 2, 5 and 10 wt.% titanium is reported. Pack boronizing of pure iron and the Fe–Ti alloys was carried out at 1100 °C for 3 h and the microstructure and the types of borides formed on the surface of pure iron and the Fe–Ti alloys substrate were studied by optical microscopy, SEM, EDS and XRD. Microhardness measurements of the substrates and boride layer formed on the substrates were also carried out. The microhardness of the boride layers were approximately 1774 HV and 1900–2220 HV for pure iron and the Fe–Ti alloys, respectively. A single boride layer of Fe 2B with saw-tooth morphology was obtained on the pure iron while a double boride layer of FeB, Fe 2B with TiB 2 as precipitates and a transition zone with TiB 2 were found on the Fe–Ti alloys. The saw tooth-like morphology changed to a compact morphology of the boride layer on Fe–Ti alloys with increasing amount of Ti. TiB 2 phase developed in the form of precipitates with different geometrical shapes. The volume and size of TiB 2 precipitates increased with increasing Ti content. The TiB 2 precipitates were distributed finely in the boride layers, but were coarser in size and with a relatively higher volume fraction in the transition zone. The thickness of the boride layer decreased exponentially with addition of Ti. The average thickness ranged between 68 µm and 320 µm for Fe–10 wt.% Ti and for pure iron respectively.