الفهرس 
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Abstract
Nickel Titanium alloy (Nitinol) is well known for its distinctive shape-memory effect and superelasticy effect beside its great resistance of corrosion and bioxmechanical compatibility. Thesexproperties have empowered its applications particularly within the bio medical and
aerospace field. Despite these exceptional properties, Manufacturing of nitinol by
conventional procedures are exceptionally troublesome and costly and consequently, must be inspected. Therefore, additive manufacturing specifically the laser-based ones were used
recently. In this thesis, Laser metal deposition (LMD) process of Nitinol was investigated in addition to the effect of process parameters on the properties of Nitinol. Preparation of the
Specimens and the tests needed to be done were carried out in The National Laser Centre in Pretoria- South Africa. The effect of Heat treatment on Nitinol’s Superelasticity, Hardness, Microstructure, and phases transformation was also evaluated. Systematic characterization of Nitinol Specimens was done utilizing Optical Microscopy, Energy dispersive X-ray analysis (EDX) and Nano-indentation test. Specimens of nitinol was synthesized with different
processing parameters using laser cladding and its properties were investigated and compared to one another to get the optimum processing parameters to synthesize a near net shape, fully dense Nitinol component with reliable properties.
At first, eight preliminary Specimens were prepared with different processing parameters in terms of laser power, scan speed and rotating speed by which the powder is deposited while keeping the spot diameter constant. The objective of preparing the first batch of Specimens was to investigate its microstructure and find which one had the martensite phase in its
microstructure.
After the Specimens were mounted, polished, and then etched, it was clearly observed that all of the Specimens have dendrite arms concentrated at the diffusion zone between the substrate and the clad layer, Specimen A (Laser power = 1.5 kW, Scan speed = 1.5 m/min, Ti/Ni 2/1.4 rpm) has cracks and pores. However, the rest of the Specimens were crack free except for Specimen (Laser power = 1.25 kW, Scan speed = 1.5 m/min, Ti/Ni 1.5/1.5 rpm) which has a crack, nevertheless, it was the most promising Specimen among the first batch that possess the
martensite phase in its microstructure and the least number of pores.
Depending on this finding, a second batch of Specimens with processing parameter near that of Specimen H was prepared to investigate its microstructure, Elemental chemical analysis,
super elasticity and Hardness so that to get a better understanding of the effect of the processing parameters on the properties of nitinol.
In the second batch of Specimens, it was clearly observed that all the Specimens have the
martensitic phase in addition to a low percentage of pores and cracks compared to the first batch of Specimens. There are two kinds of pores found, one has a circular shape and it’s due to the gasses trapped or the Nickel evaporation that happens during the process, another kind of pores was the irregular pores that occur due to the lack of complete melting. The cracks found were due to the residual stresses that happen due to the temperature gradient present in the process.
The dendrites which are a metastable phase that should have transferred into Ni Ti were found in this batch too, however, Specimen four (Laser power = 1.25 kW, Scan speed = 1 m/min, Ti/Ni 1.5/1.5 rpm) which has the highest Laser energy density, has the lowest number of
dendrites and this leads to the conclusion that increasing the laser density decreases the number of dendrites.
The results showed that there’s a processing parameter window at which the alloy possess its best functional properties and microstructure that possess 40% volume fraction of martensite which is at a laserxpower of 1.25 kW, and a Scan Speed of 1.5 meter.〖min〗^(-1) and feed rate of 1.5/1.5 RPM, depending on these conditions another batch of Specimens was prepared with a narrowed down processing conditions that led to a more optimum conditions of laser power 1.25kW , scan speed of 1.5m/min and feed rate of 1.9/1.5 rpm at which nitinol possessed the martensite phase and good superelasticity and it had an almost 50-50%atomic Ni/Ti , and then on these conditions performing heat treatment of heating till 400 ℃ and keeping in the furnace for five minutes and then cooling in atmospheric conditions enhanced greatly the functional and Hardness