Babatunde Abiodun Obadele

Influence of spark plasma sintering on microstructure and wear behaviour of Ti-6Al-4V reinforced with nanosized TiN

Abstract Ti-6Al-4V/TiN composites were successfully consolidated by spark plasma sintering (SPS). TiN addition to Ti-6Al-4V was varied from 1% to 5% (volume fraction). The effect of TiN addition on the densification, microstructure, microhardness and wear behaviour of Ti-6Al-4V was studied. Experimental results showed reduction in sintered density of the compacts from 99% to 97% with increase in TiN content. However, an increase in microhardness value was recorded from HV0.1 389 to HV0.1 488. X-ray diffraction (XRD) analysis showed that the intensity of diffraction peaks of TiN phase in the composites increased also with formation of small amount of secondary Ti2N phase. SEM analysis of SPS sintered nanocomposites possessed a refinement of α/β phase microstructure in Ti-6Al-4V with the presence of uniformly dispersed TiN particles. The worn surface of the composite showed improved abrasive wear resistance with non-continuous grooves as compared to the sintered Ti-6Al-4V without TiN addition.

Effect of TiN and TiCN additions on spark plasma sintered Ti–6Al–4V

Abstract In this study, the microstructural and densification behavior of titanium nitride (TiN) and titanium carbonitride (TiCN) reinforced Ti-6Al-4V were investigated under an applied pressure of 50 MPa, sintering temperatures of 1000–1100 °C, heating rate of 100 °C/min and dwell time of 10–20 min through spark plasma sintering technique. Results show that the microstructural transformation of the titanium matrix composite comprises of a mixture of lamellar colonies with β grain boundaries and nanoparticles with an average grain size range of 4.5–6.0 μm. Furthermore, an addition of nanoceramics TiN/TiCN resulted in microstructural transformation, uniform particle distribution within the metal matrix and along the grain boundary. However, the sintered relative density of the composites decreased with the percentage increase in TiCN, while fully dense composites were obtained at a sintering temperature of 1100 °C. Microhardness values of the sintered composites reach a greater level in comparison to Ti-6Al-4V alloy while fracture morphology of the sintered composites with addition of nanoceramics (TiN/TiCN) displayed a transgranular transformation within the matrix accompanied with fine dimple features.

Influence of Shear Stress on Erosion–Corrosion of Stainless Steels in Simulated Mine Water

This study provides information on the performance of three stainless steels at various shear stresses and presence of silica sand particles in simulated mine water. The materials employed were two duplex stainless steels (UNS S32205 and UNS S32750) and one austenitic stainless steel (UNS 30403). The rotating cylinder electrode system produced shear stresses to evaluate the flow-induced and erosion–corrosion tests by open-circuit potential and potentiodynamic polarization techniques. Hardness tests were used to examine the performance of the degraded samples, and scanning electron microscopy was used to characterize the surface morphology. UNS S32750 displayed nobler OCP compared with UNS S32205 with austenitic steel having the least potential irrespective of the shear stresses and with/without silica sand. Work hardening of the duplex stainless steels promoted variable behavior in the hardness results. The current density results revealed that UNS S32705 had the best corrosion performance in the studied environments. The SEM images showed plastic deformation, material dissolution and pitting corrosion as the shear stress increased and on the introduction of silica sand.

Synthesis of Ti-6Al-4V alloy with nano-TiN microstructure via spark plasma sintering technique

The effect of nano-TiN dispersion strengthened Ti-6Al-4V via spark plasma sintering method has been investigated. Ti-6Al-4V with 4 vol. percent of nano-TiN were mixed in a Turbula shaker mixer for 8 h at a speed of 49 rpm and the admixed powders were sintered at sintering temperature range of 1000 - 1100 °C, holding time of 10-30 mins, heating rate of 100 °C/min under an applied pressure of 50 MPa. The morphology of the as-received and sintered compacts was examined by scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS) and phase analysis was done by X-ray diffractometry (XRD). The sintered compacts without nano-TiN reveal lamellar structure while reinforced Ti-6Al-4V with nano-TiN shows a bimodal structure and titanium nitride has a great influence on a grain growth at high temperature. Furthermore, the microstructural formation mechanism was investigated. With the addition of the content of Ti-6Al-4V with 4 vol.% of nano-TiN, the micro-hardness also improved and this was due to homogenous distribution of TiN in Ti-6Al-4V matrix.

Corrosion behaviour of Al-Fe-Ti-V medium entropy alloy

Alloys containing up to four multi-principal elements in equiatomic ratios are referred to as medium entropy alloys (MEA). These alloys have attracted the interest of many researchers due to the superior mechanical properties it offers over the traditional alloys. The design approach of MEA often results to simple solid solution with either body centered cubic; face centered cubic structures or both. As the consideration for introducing the alloys into several engineering application increases, there have been efforts to study the corrosion behaviour of these alloys. Previous reports have shown that some of these alloys are more susceptible to corrosion when compared with traditional alloys due to lack of protective passive film. In this research, we have developed AlFeTiV medium entropy alloys containing two elements (Ti and Al) that readily passivate when exposed to corrosive solutions. The alloys were produced in vacuum arc furnace purged with high purity argon. Open circuit potential and potentiodynamic polarisation tests were used to evaluate the corrosion behaviour of the as-cast AlFeTiV alloy in 3.5 wt% NaCl and 1 M H2SO4. The corrosion performance of the alloy was compared with Ti-6Al-4V alloy tested under similar conditions. The results show that unlike in Ti-6Al-4V alloy, the open circuit potential of the AlFeTiV alloy move towards the negative values in both 3.5 wt% NaCl and 1 M H2SO4 solutions indicating that self-activation occurred rapidly on immersion. Anodic polarisation of the alloys showed that AlFeTiV alloy exhibited a narrow range of passivity in both solutions. In addition, the alloys exhibited lower Ecorr and higher Icorr when compared with traditional Ti-6Al-4V alloy. The traditional Ti-6Al-4V alloy showed superior corrosion resistant to the AlFeTiV alloy in both 3.5 wt.% NaCl and 1 M H2SO4 solutions.