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WED machinability of a 25% silicon carbide particle reinforced 6061/Al alloy composite
No full textWire Electro Discharge Machining is used for the processing of heat treated high quality alloys or for the machining of complex shapes of advanced materials. Results on the machinability performances of a 25% SiC particle reinforced Al 6061 T6 composite and of the Al 6061 alloy by both roughing and finishing methods are given. Machining tests were performed with the following parameters: 1) peak current 16, 32, 64 A; 2) pulse duration 1.6, 6.4 ms; 3) voltage 120 V; 4) wire SW25X, 0.25 mm diameter, Charmilles Technology. The machined surfaces were observed at the SEM using both secondary electrons (SE) and back-scattered electrons (BSE). EDAX semi-quantitative analyses were also carried out. The surface features, roughness, hardness and contamination for the process parameters used are pointed out. Results are compared with the ones obtained machining the base Al 6061 T6 Allo
On the perfoemance of a CRN coated SIC whiskers reinforced ceramic tool high speed machining of NI-base super-alloys
No full textThe main limitation on the wider use of Nickel-base super-alloys, such as INCONEL 718 (UNS N07718) is the difficulty in conventional-type machining. Even the expensive SiC whiskers reinforced ceramic tools, that are more suitable for use at high cutting speeds, have a short life-time. The aims of the study is to obtain an increase in tool life by minimising the temperature effects on composite reinforcement mechanisms. 20% SiC whiskers reinforced Al2O3 tools were CrN coated by PVD. Comparative machining tests on INCONEL 718 were performed using 20% SiC whiskers reinforced Al2O3 tools and CrN coated 20% SiC whiskers reinforced Al2O3 ones. After 40 and 60×10-6 m3 alloy removal the tools were observed at SEM and EDAX semiquantitative analyses were carried out. The CrN layer behaviour under the various cutting conditions used was analysed. Different wear mechanisms along tool chip contact length were observed. The causes and the mechanisms of wear were deduced and a mathematics model linking tool life with process parameters is suggeste
Meccanismi di Usura di Utensili Ceramici Rinforzati con Whiskers di SiC nalla Lavorazione ad Alta Velocità di Inconel 718 e Acciaio C40
No full textFatigue fracture of AISI 4340 DVM steel in gaseous hydrogen & effect of tempering temperature
No full textThe effect of dry hydrogen (p = 102 kPa at room temperature) on AISI DVM austenized at 1113 K and tempered at 463, 53 and 743 K has been investigated by means of determinations of fatigue crack growth rate (FCGR) using CT samples (L-R and C-L orientation) precracked in laboratory air up to a value of ΔK of about 11 MPa√m. The fatigue tests were conducted both in air (RH = 45-50%) and hydrogen environment under the following conditions: R = 0.2, Pmax = 2.5 kN, sine wave of 3 and 0.5 Hz. The FCGR were found to be independent on the frequency. The fracture surface of samples fatigated in air, showed brittle striations and, at higher ΔK, some transgranular fracture, while in those obtained in dry hydrogen both an increasing percentage of quasi-cleavage facets and secondary cracks were observed. The fatigue behaviour of the specimens tempered at 463 and 553 K in the two environments considered was much diversified. The fracture surfaces revealed a mixed fracture mode: intergranular along the grains of primary austenite and in some zones, transgranular. The da/dN - ΔK curves showed that the FCGR was controlled by a condition of stress corrosion cracking. A KISCC value of 13.7 MPa√m was estimated. The appearance of a plateau in these curves, at nominal increasing ΔK, is presumably attributable to a slowing of the primary cracking owing to the occurrence of an increasing number of secondary cracks
On the perfoemance of a CRN coated SIC whiskers reinforced ceramic tool high speed machining of NI-base super-alloys.
No full textThe main limitation on the wider use of Nickel-base super-alloys, such as INCONEL 718 (UNS N07718) is the difficulty in conventional-type machining. Even the expensive SiC whiskers reinforced ceramic tools, that are more suitable for use at high cutting speeds, have a short life-time. The aims of the study is to obtain an increase in tool life by minimising the temperature effects on composite reinforcement mechanisms. 20% SiC whiskers reinforced Al2O3 tools were CrN coated by PVD. Comparative machining tests on INCONEL 718 were performed using 20% SiC whiskers reinforced Al2O3 tools and CrN coated 20% SiC whiskers reinforced Al2O3 ones. After 40 and 60×10-6 m3 alloy removal the tools were observed at SEM and EDAX semiquantitative analyses were carried out. The CrN layer behaviour under the various cutting conditions used was analysed. Different wear mechanisms along tool chip contact length were observed. The causes and the mechanisms of wear were deduced and a mathematics model linking tool life with process parameters is suggested
WED machinability of a 25% silicon carbide particle reinforced 6061/Al alloy composite
No full textWire Electro Discharge Machining is used for the processing of heat treated high quality alloys or for the machining of complex shapes of advanced materials. Results on the machinability performances of a 25% SiC particle reinforced Al 6061 T6 composite and of the Al 6061 alloy by both roughing and finishing methods are given. Machining tests were performed with the following parameters: 1) peak current 16, 32, 64 A; 2) pulse duration 1.6, 6.4 ms; 3) voltage 120 V; 4) wire SW25X, 0.25 mm diameter, Charmilles Technology. The machined surfaces were observed at the SEM using both secondary electrons (SE) and back-scattered electrons (BSE). EDAX semi-quantitative analyses were also carried out. The surface features, roughness, hardness and contamination for the process parameters used are pointed out. Results are compared with the ones obtained machining the base Al 6061 T6 Alloy
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