Boron carbide particles can reduce the wear of the composite material by increasing its hardness, but they do not affect the oxidation of the magnesium matrix in any way. The oxidation rate of magnesium depends only on the environment (oxygen content, humidity, etc.) and on temperature. On the other hand, a possible positive effect of the presence of solid particles in the magnesium matrix may be that due to a decrease in the coefficient of friction, the surface temperature will also decrease.

Sir Vadim Verlotski, I appreciate your explanation. As you said, the presence of boron carbide can reduce the friction coefficient and surface temperature of mating bodies. I'm asking that if there was an oxidation mechanism in the unreinforced magnesium alloy, might adding reinforcing particles result in oxides reduction during sliding wear due to a lower surface temperature?

Theoretically, everything is correct: if the friction temperature decreases (due to a decrease in the coefficient of friction), then oxidation of the surface will also decrease. I cannot say how it will look in practice, since the friction temperature depends on many factors.

Dear Seyed Masih Banijamali

Pure Mg oxidized naturally in air, forming a surface product of MgO, MgCO3 and traces of Mg, as the matrix surfaces is continuously contaminated by free carbon from the air. In case of oxidative wear mechanism under mild sliding friction in normal air atmosphere, H2O molecules and carbon atoms can easily attached to the tribo-film on the worn surface and so allowed formation of oxide layer consisting of Mg(OH)2•nH2O, MgCO3 and MgO. This layer has lubricating and protective properties and found able to protect the worn surface and so minimizing the impact of surface oxidative wear.

Now, when adding B4C to Mg as reinforcing particles, two cases I can put to cover the role of this addition in affecting the oxidative wear mechanism in terms of oxidation rate by either promoting or inhibiting its rate.

In the first when absolutely pure B4C is added to Mg, no effects will raise while with second case, where commercial B4C used which is normally contaminated with free carbon. This carbon will found in the tribo-oxide layer on the worn surface, sharing the tribo-chemical reaction in that allowing the formation of MgCO3 in stead of sharing the free carbon from the air which is very slow route. So only with this case the oxidative wear process being much inhibited.

Best regards

Thank you for your detailed explanation, Mr. Mohammed Hussein j. H. Al'Atia

Is it acceptable to use XRD to examine the formation of mentioned MgCO3 phase from generated wear debris?

Dear Seyed Masih Banijamali

Thank you for your kindly feedback.

It is not easy to characterize the formation of MgCO3 as single phase pattern from generated wear debris by XRD, while by FT-IR analysis may become easier to observe the bands of CO3−2 in MgCO3 at 1559 cm−1 and 1541 cm−1.

Best regards

Hello Mr. Mohammed Hussein j. H. Al'Atia

I would want to thank you again for your thorough response to my query.

Per your suggestion, we have performed an FT-IR analysis on generated wear debris for both Mg alloy and its composite with B4C particles. The detected tribochemical compounds were MgCO3, Mg(OH)2, and MgO. As anticipated, the CO32- bands in MgCO3 increased. Now, I would appreciate it if you could clarify why increasing CO32- bands in composites might lessen their oxidative wear probability.

Best regards

Dear Seyed Masih Banijamali

Thank you for your kindly feedback.

Yes, this is because MgCO3 is the mainstay compound in the oxide layer composition that affecting it's integrity and so obtaining higher protective level . Therefore, increasing in MgCO3 content makes oxide layer has higher lubricating and protective properties and able to protect the worn surface and so lessen the impact of surface oxidative wear.Hope you success and progress with best regards