Wear of Hard Chrome Plating

[bakgun1981]

Hi everyone. I'm a senior designer with 13 years of design experience in aerospace industry.

I'm gonna ask you about a finishing problem of a part. We have a mechanism with a clevis arm and a lug arm. The joint between them is spherical by bearing. Also there is a spring arm beside the arms that forces lug touching on clevis from side, as much as spherical bearing permits.

Because this feature forces two materials contact with high load, we hard chrome plated the lug arm end. Then put a special bushing with wide head that limiting the movement of the spherical joint. We also plated hard chrome this bushing as well.

After some cycles of loading, we saw that bushing and lug arm has a big wear.

What do you offer for such an application ?

* We both hard chrome plated lug and bushing. Is it correct to plate same material under high wear risk ?
* Do we need to change finish of one of them ? Or do we need to change one material to heat treated instead of hard chrome plating ?

Both materials are 15- 5 PH H1025 cres and both platings are hard chromium.

Thanks & Best Regards

[Cragyon]

Chrome plating is not meant for friction or sliding. Can you design in a bushing for the contact surfaces..

[JAlberts]

The problem is that no matter the precision or finish there are going to be small imperfections in thee base material that will translate through the chrome to its surface on both components. So since both mating surfaced are hardened there will always be small to minute areas of extremely high contact pressure that will start to breakdown and possibly start to fracture the hard chrome plating and result in sharp chrome edges starting to wear on the adjacent contact surface.
What is needed is a differential hardness between the two surfaces that will allow one of them to yield sufficient to spread those point contact stress areas with damaging the surface. One such arrangement would a hardened surface in contact with bronze insert sleeve, preferably a porous self lubricating bushing; however, the joint must then be designed so as provide a bearing load area that is consistent with the capabilities of the lower hardness sleeve.
You have stated that this is very high load joint so, while I would normally also suggest some version of a filled polymer material for the sleeve but that may not be possible for your very high loading condition.
Har chrome can be used fo one of the bearing surfaces but only when mated with a softer compliant surface such as I described above.