45C and 45VF by APS

[derek]

Hi Gordon, have you got any chance to spray 45C and 45VF by SG-100 gun? What kind of parameter did you use to spray these powders? It seems that OEM's parameter is not perfect. My problem is for 45C we got too much oxide and for 45VF we got too much porosity.
I appreciate your help.

[Gordon]

Hi Derek
I have not had any first hand experience of using the SG-100 gun, but I will give some guidance that should be common to most plasma spray equipment.

Before making any parameter changes, make sure your equipment is in good working order and recently serviced and calibrated. Also, check that your coating metallography testing procedure is in fact giving true results. Be warned, I've seen this many times where people waste time,effort and resources trying to optimize process parameters, only to find that equipment or coating test results were the initial cause of their problem.

In the case of 45C with too much oxide, we could assume that the powder is receiving too much heat during spraying. To reduce the heat input, I would initially try reducing (in small steps) the secondary plasma gas flow only. This should have a fairly dramatic effect, reducing the plasma voltage and plasma energy. Another approach would be to increase the primary plasma gas flow, which will in fact slightly increase plasma voltage and energy, but may also increase plasma velocity, resulting in a lower particle dwell time in the plasma and less heat input to the powder.

In the case of 45VF with too much porosity (possibly too many ?unmelts?), we could assume the opposite to the case above, where the powder is not seeing enough heat and basically the reverse procedure will be required.

I must stress that this is a very complex matter and I've made certain basic assumptions that could be incorrect. Try a few of the parameter changes above and see how they effect your coating, then at least you may know if your going in the right direction in improving your coatings.