Effect of cryogenic treatment applied to M42 HSS drills on the machinability of Ti 6Al 4V alloy

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This study investigated the effects of deep cryogenic treatment applied to M42 HSS drills on the tool wear, the tool life and the surface roughness during the drilling of a Ti-6Al-4V alloy under dry and wet cutting conditions.Drilling tests were carried out using untreated, cryogenically treated, cryogenically treated and tempered, and multi-layered TiAlN/TiN-coated HSS drills.Four different cutting speeds ((6, 8, 10, 12) m/min) and a constant feed rate of 0.06 mm/r were used as the cutting parameters and holes with a depth of 15 mm were drilled.At the end of the drilling tests, it was seen that the use of a coolant increased the tool life and decreased the surface roughness.Among the four tools, the best results in terms of the tool life and surface roughness were obtained with the multi-layered TiAlN/TiN-coated tool.The cryogenically treated and tempered drills exhibited an increase of 87 % in the tool life compared to the untreated drills.Scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses showed that by reducing the size of the carbide particles in the microstructure, cryogenic treatment resulted in a more uniform carbide distribution and in the transformation of retained austenite to martensite.This played an important role in the increase in the hardness and wear resistance of the cutting tools.Keywords: cryogenic treatment, microstructure, M42 HSS, drilling, tool life, surface roughness V tej {tudiji je bil preiskovan vpliv globokega podhlajevanja svedrov M42 HSS na njihovo obrabo, zdr`ljivost in hrapavost povr{ine med suhim in mokrim vrtanjem zlitine Ti-6Al-4V.Preizkusi vrtanja so bili izvr{eni z uporabo HSS neobdelanih, podhlajenih, podhlajenih in popu{~anih ter svedrov z ve~plastnim nanosom TiAlN/TiN.Uporabljene so bile {tiri razli~ne hitrosti rezanja ((6, 8, 10, 12) m/min) in konstantno podajanje 0,06 mm/r pri vrtanju 15 mm globokih izvrtin.Na koncu preizkusov vrtanja se je pokazalo, da uporaba hlajenja s teko~ino pove~a zdr`ljivost orodja in zmanj{a hrapavost povr{ine.Med {tirimi orodji je bil glede na njihovo zdr`ljivost in hrapavost povr{ine najbolj{i rezultat dose`en z orodji z ve~plastnim nanosom TiAlN/TiN.Podhlajeni in popu{~ani svedri so imeli pove~ano zdr`ljivost za 87 % v primerjavi z neobdelanimi svedri.Analize na vrsti~nem elektronskem mikroskopu (SEM) in rentgenska difrakcija (XRD) sta pokazali, da z zmanj{anjem velikosti karbidnih zrn v mikrostrukturi pri podhlajevanju dobimo bolj enakomerno razporeditev karbidov, preostali avstenit pa se pretvori v martenzit.To ima pomembno vlogo pri pove~anju trdote in odpornosti orodja za rezanje proti obrabi.