> According to SAE paper 860560
     > "Material Technology Development Applied to Rotary Engines at Mazda".
     >
     > The alloy used for the rotor housing is JIS AC4D Si 5.0% Cu 1.2% Mg 0.5%
     > Heat treated to T6.
     >
     > Sounds like high silicon low thermal expansion alloy ot me.
     >
     > The number of cycles is not necessarily related to real world
     > as a torture test was devised.
     >
     > Paul Lamar

     Mazda devised a very simple machine to test the durability of various rotor housing
     coatings.

     My theory is the stiffness of the underlying material has a large
     affect on the durability of the coating and the formation of chatter marks.
     Apex seal chatter is a vibration and as such it is affected by the
     mass of the apex seal and the spring rate of the material it is rubbing
     against. Steel is three times stiffer than aluminum so steel showed a significantly
     advantage in this test IMHO. It was called the SIP (Sheetmetal Insert Process).

     Here is what Mazda had to say about it.

     "CHROME PIATING - Rubbing by the apex seal used to cause the
     trochoid surface to develop the so-called chatter mark - ripple marks
     and scuffing.

     To overcome this problem, study was made on material of the apex seal and
     chrome plating of the trochoid surface.

     The electroplating procedures studied for surface-treating the trochoid
     surface included nickel plating containing silicon carbide, cermet spray,
     and chrome plating, and this last was adopted for quality and productivity.
     The chrome plating has a Vickers hardness of more than 1100. Furthermore,
     the chrome plating, which is characteristically poor in wettability with
     oil, is provided on its surface with minute pores. and channels for
     effective oil retention,

     As shown in Fig. 6, the chrome-plated surface is given electro etching and
     honing to make it pinpoint-porous, followed by another electro etching
     which produces micro-channels [1]*. This micro-channel porous (MCP) plating
     is effective in maintaining oil film and reducing the friction with the apex
     seal."

     Paul Lamar

William wrote:

I was wondering if a coating of titanium nitride on the wear surfaces would work.

To my knowledge it has not been tried yet. Certainly seems to work great
on cutting tools. Might be easy to apply to the apex seals themselves.

Paul Lamar
 
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