problems with T800 HVOF

[Gordon]

Hi Erick

Good to hear you are making steady progress. Nothing like getting stuck into a difficult coating development trial to expand your knowledge and learning on thermal spray coatings

[erick212]

Ya, it felt great to make huge strides and break away from the conventional thinking that my co-workers were using. I am not new to thermal coatings, I've been in the biz for 14 years. I'm just new to HVOF, it is a very different animal than other processes. I now have an acceptable round robin test ready to go out to the independant lab for correlation. This was done with the DJ2600, O2 and hydrogen as fuel gas. The 2 biggest factors were standoff and hydrogen %. The first test there was too much heat and to much time in the flame. After the adjustments we were getting great micro, hardness(micro and macro) and tensile pulls well over 10,000psi. Oh, and another tidbit I found almost no difference from the Praxair powder to the Stellite powder.


Erick

[wgg237]

Hi Erick

No pre-heating I would have thought a pre-heat would benefit bond strength, unless you are having trouble controlling coating/substrate temperature during spraying.

Are your bond strength test pieces sprayed under simulated conditions of that of the actual component parts or is it just general proving of process/powder?

Well here it is.. I have a good micro and good bond pulls. The parameter that was recommended was making the coating way to brittle.I did micro hardness and was fracturing the coating with the diamond @ a 300g load(I had to use a 100g to get anything ) I lowered the H2 and O2 and that made a huge differance. The coating structure is great, the hardness is a little towards the low side(i'm workning on that), the oxides are great..... now for the best part.... my tensile pulls are now in the 9 to 10k range. As for preheat I found that it made a slight increase in tensile readings with no preheat. This was over 20 runs of data review. This testing is just to prove powder/process. I will be doing this again in a few days... I just setup another HVOF booth and it should be running today or tomorrow.

Erick

Hi Erick,

Based on your description, it seems that you have a great improvement in T800 HVOF. what are the key parameters(e.g. distance, fuel/oxygen ratio etc.) to tensile bone strength(TBS)? The best TBS I got is now in the 5 to 6K range. I need to improve it to around 9K.