ساخت و مشخصه يابي نانو كامپوزيت Fe,Cr)3Al-20%vol.Al2O3) به روش مكانوشيميايي

Mechanochemical synthesis of (Fe,Cr)3Al–20%vol.Al2O3 nanocomposite

در اين پژوهش نانو كامپوزيت Fe,Cr)3Al-20%vol.Al2O3)، توسط فرايند آلياژسازي مكانيكي مخلوط پودري هماتيت، آهن كرم و آلومينيوم بصورت درجا توليد شد. در مخلوط پودري فوق، نسبت هاي استوكيومتري به گونه اي انتخاب شد كه درصد اتمي عناصر آهن، آلومينيوم و كرم در تركيب Fe,Cr)3Al)، به ترتيب 50 و 25 و 25 باشد. تغييرات ساختاري ذرات پودر در حين فرايند الياژ سازي مكانيكي توسط آزمون پراش پرتو ايكس مطالعه و بررسي شد. نتايج حاكي از آن است كه مخلوط پودري آهن، كرم و آلومينيوم و هماتيت با گذشت زمان آسياب كاري و انجام واكنش مكنوشيمايي به محلول جامد (Fe(Cr,Al و فاز Al2O3 تبديل مي شود. در زمان هاي بالاتر آسياب كاري محلول جامد (Fe(Cr,Al به تركيب بين فلزي Fe,Cr)3Al) نانو ساختار تبديل مي شود. سپس از ذرات پودر نانو كامپوزيتي Fe,Cr)3Al-20%vol.Al2O3)، توسط فرايند پرس ايزواستاتيك سرد و سينترينگ در دماي 1400 درجه سانتيگراد و به مدت يك ساعت نمونه هاي بالك تهيه گرديد. ريز ساختار سطح مقطع نمونه هاي سينتر شده، توسط ميكروسكوپ الكتروني روبشي مورد بررسي قرار گرفت و بررسي سطح مقطع نانو كامپوزيت فشرده شده آزمون ريز سختي سنجي انجام شد.

Iron aluminides have received considerable attention as a structural material because of their advantageous properties, in particular, high specific strength, relatively high wear resistance and hardness, high melting point, high oxidation and corrosion resistance. However, industrial application of these alloys has been limited due to their brittleness at room temperature and their poor creep resistance above 600 °C. Several approaches were attempted to improve their major drawbacks such as reducing the grain size to nanometric range, dispersion strengthening and addition of alloying elements such as Cr. Taking all these factors into account, the synthesis of particulate reinforced FeAl(Cr) intermetallic compound composite with nanostructured matrix can be interesting. The reinforcement particles can be either directly added to the matrix (ex-situ technique) or formed by an in-situ displacement reaction. One possible route for in-situ introducing hard particles in the matrix of composites is the mechanochemical processing in which high-energy milling promotes the displacement reaction in a mixture of reactive powders. In this study, fabrication and formation mechanism of alumina reinforced (Fe,Cr)3Al matrix nanocomposite via mechanochemical processing have been investigated. (Fe,Cr)3Al-20vol.%Al2O3 nanocomposite were fabricated using ball milling of Fe-Al-Cr-Fe2O3 powder mixture. The structural evaluation of powders was studied by X-ray diffraction (XRD). Results showed that milling of Fe-Al-Cr-Fe2O3 powder mixture led to the formation of (Fe,Cr)3Al-Al2O3 nanocomposite by gradual reduction of Fe2O3 by Al. Then (Fe,Cr)3Al-20vol.% Al2O3 nanocomposite powder was isostatically cold pressed and sintered at 1400 °C for 1 hour. The consolidated part had an ultrafine uniform structure consisting of an interconnected network of (Fe,Cr)3Al and Al2O3 phases. This structure had a hardness value of 626 Hv which is much higher than that for similar material fabricated by other methods.