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This aim of this research is to investigate the impact of laser power on the hardness and the wear resistance properties of laser metal deposited 17-4 PH stainless steel. Hardness was studied using the Zwick/Roell microhardness tester and the wear resistance property was carried out using the ball-on-disc Anton Paar-tribometer wear tester. The study revealed that an irregular increase and decrease in the average hardness value and wear behaviour were observed. This could be attributed to the presence of copper precipitate which was more concentrate at the overlapping region because of the reheating activity that is happening between the succeeding and preceding track layers.

This study investigates the influence of the quantity of tungsten powder on the microstructural evolution of 17-4 PH stainless steel-tungsten composite produced using laser metal deposition process. The 17-4 PH stainless steel and tungsten powders were deposited on 316 stainless steel substrate at laser power of 2600 W. The tungsten powder flow rate was varied between 0.5 rpm and 2.0 rpm while 17-4 PH stainless steel powder flow rate, the scanning speed, the gas flow rate and the laser spot size were fixed at 2.0 rpm, 0.5 m/s, 2.5 l/min and 2.0 mm respectively. Five (5) multiple tracks of 17-4 PH stainless steel and tungsten powder were deposited on 316 stainless steel of 10 mm thickness from different hopper at 50% overlapping percentage to produce 17-4 PH SS-W composite. During the microstructural study, it was observed that tungsten carbide has been precipitated in-situ and evenly dispersed in the 17-4 PH SS-W composite produced. SEM and EDS analyses also revealed the presence of BCC alpha (α) ferrite and FCC gamma (δ) ferrite with the presence of sigma (σ) phase precipitates.

In this study, the application of characteristic impedance in estimating specific energy and average fragment size of rocks was investigated during rock breakage at high strain rates. To achieve this, rock specimen was prepared in accordance with recommendations of the International Society for Rock Mechanics and broken at high strain rates using the split Hopkinson’s pressure bar system. Results reveal that although strain rate is well related to specific energy and average fragment size of broken rocks, the product of characteristic impedance and strain rate is more reliable for estimating the forementioned parameters. In addition, strain rate and dissipated energy generally increase at higher incident energies while the average fragment size of broken rocks reduces at higher strain rates. Based on these findings, more studies on indirect estimation of energy requirement for rock breakage to desired average fragment sizes is recommended from the product of characteristic impedance and strain rate.

This research studies the wear behavior of laser metal deposition of 17-4 PH SS-W composite using a 6 mm alumina-stainless steel ball under a load of 10 N, for 16 minutes, 40 seconds and with acquisition rate of 100 Hz conducted at 25°C. The effect of laser power of between 2600 W and 1500 W; and powder flow rate of between 0.5 min À 1 and 2.0 min À 1 on wear resistance is investigated. Other processing parameters are constant throughout the experiments. The results show that the 17-4 PH SS-W composite produced at a high laser power of 2600 W exhibits a higher wear resistance as compared to the 17-4 PH SS-W composite samples produced at low laser power of 1500 W. The 17-4 PH SS-W composite sample produced at high laser power of 2600 W with tungsten powder flow rate of 2.0 min À 1 has the highest wear resistance with wear volume of 0.0276 mm 3 and wear rate of 8.8 · 10 À 5 mm 3 /N m while the 17-4 PH SS-W composite sample produced at a low laser power of 1500 W with tungsten powder flow rate of 1.0 min À 1 has the wear volume of 0.02834 mm 3 and wear rate of 9.0 · 10 À 5 mm 3 /N m. Keywords: Ball-on-disc / sliding wear / 17-4 PH SS-W composite / wear volume / wear rate Diese Forschung beinhaltet das Verschleißverhalten von mit dem Laserstrahl aufgetragenen Metall-Verbundwerkstoffen (17-4 PH SS-W) unter Verwendung einer 6 mm Aluminiumoxid-Edelstahlkugel unter einer Last von 10 N für 16 Minuten und 40 Sekunden und mit einer Erfassungsrate von 100 Hz bei 25°C. Es wurde die Wirkung der Laserleistung zwischen 2600 W und 1500 W und die Pulverflussrate zwischen 0,5 min À 1 und 2,0 min À 1 auf die Verschleißfestigkeit untersucht. Andere Verarbeitungsparameter sind während der Experimente konstant. Die Ergebnisse zeigen, dass der 17-4 PH SS-W-Verbundstoff, der bei einer hohen Laserleistung von 2600 W hergestellt wurde, eine höhere Verschleißfestigkeit aufweist als die 17-4 PH SS-W-Verbundproben, die bei einer niedrigen Laserleistung von 1500 W