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Cold Spray Additive Manufacturing

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    Since the share price is not going anywhere meaningful for the time being, I thought I'll share some of my research on Cold spray/supersonic particle deposition (SPD) Additive manufacturing. I tumble across this free to access review article on Researchgate (link below) that describe everything we need to know about SPD AM. Don't worry it is not hard to follow what was written in the article, you don't need to be a material scientist to understand, I am not one myself.

    Here are what I find interesting about SPD AM:
    1) We know that TKF can produce titanium products that are 83% high strength and 38% higher elongation than ASTM for titanium parts using grade 2 pure titanium powder, But what about alloys? How different metals join together during SPD without heat treatment? I found the answer in Figure 6.

    "...When a single particle is fired at the substrate, the particle impacts and penetrates the substrate. Some interlocking occurs at the rim of the particles, but there is no intermetallic bonding. However, when additional particles are fired, the peening effect cracks the oxide layer, and metal can flow out of the broken cracks, creating metal-to-metal bond-ing [41]. Xie et al. [41] further explained that due to the “par-ticle peening”or tamping, metal-to-metal bonds exist in SPD with multiple particles (Fig. 6b), but not in single-particle sprays (Fig. 6a)."

    2) Cold sprayed material is more porous, leading to lesser tensile strength. But post processing significantly increased its strength.

    3) How can we solve the high porosity problem?

    by adding large peening/heavier particles into powder, the large particle can act as a hammer to hammer down the added layers. Since the larger particle will have a different acceleration when come out of the nozzle, scientist can choose a material that will fall off after impact, thus compressing the added layer without bonding it.
    For example:
    "Luo et al. [25] explained that SPD could be used as an oxide-free additive manufacturing process for metal parts. It can be challenging to obtain dense coating in relatively hard mate-rials such as “Inconel 718 superalloy”when using the cheaper nitrogen gas. However, with the inclusion of bigger stainless-steel particles, the bigger particles hammer the smaller particles, thus forming a denser coating. By including 50% by weight of bigger particles, Inconel coating porosity dropped from 5.6 to 0.26%, resulting in greater inter-particle bonding of the Inconel 718 superalloy as shown in Fig. 15"

    In conclusion:
    Cold spray/supersonic particle deposition additive manufacturing is a cost effectively way of material manufacturing and to combine different materials (metals, ceramic and polymers). The printed material is more porous, though this can be addressed by peening. Post processing (heat treatment) can also help with material bonding, increasing the tensile strength, reducing hardness, but I suspect will reduce ductility/elongation and becoming more brittle.

    I am not a material engineer so my understanding is limited to what is shown in this paper. I may not have the ability discern the validity of the science. DYOR
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