Effect of milling and annealing on microstructural, electrical and magnetic properties of electrodeposited Ni-11.3 Fe-1.4w alloy

Abstract

A nanostructured Ni-11.3Fe-1.4W alloy deposit was obtained from an ammonium citrate bath at a current density of 600 mAcm-2. XRD analysis shows that the deposit contains an amorphous matrix having embedded nanocrystals of the FCC phase of the solid solution of Fe and W in Ni with the average crystal grain size of 8.8 nm. The deposit has a high internal microstrain value and a high minimum density of chaotically distributed dislocations. The effect of milling and annealing of the Ni-11.3Fe-1.4W alloy on electrical and magnetic properties was studied. Structural changes in the alloy take place during both annealing and milling. Upon deposition, the alloy was heated to 420ºC. Heating resulted in structural relaxation which induced a decrease in electrical resistivity and an increase in magnetic permeability of the alloy. Further heating of the alloy at temperatures higher than 4200C led to crystallization which caused a reduction in both electrical resistivity and magnetic permeability. The milling of the alloy for up to 12 hours caused a certain degree of structural relaxation and crystallization of the alloy. The increase in crystal grain size up to 11 nm and the partial structural relaxation induced a decrease in electrical resistivity and an increase in magnetic permeability of the alloy. Heating the powders obtained by milling at 4200C led to complete structural relaxation, reduced electrical resistivity, and increased magnetic permeability. During heating of the powders obtained by milling at temperatures above 420ºC, crystallization and a significant increase in crystal grain size occurred, leading to a reduction in both electrical resistivity and magnetic permeability. The best magnetic properties were exhibited by the alloys milled for 12 hours and annealed thereafter at 420ºC. In these alloys, crystal grains were found to have an optimum size, and complete relaxation took place, resulting in a maximum increase in magnetic permeability.

Nanostrukturni depozit legure Ni-11,3Fe-1,4W dobijen je elektrodepozicijom iz amonijačno-citratnog kupatila na gustini struje 600 mAcm-2. XRD analiza je pokazala da se depozit sastoji od amorfne matrice u kojoj su smešteni nanokristali FCC faze čvrstog rastvora Fe i W u Ni čije su prosečne dimenzije 8,8 nm. Proučavan je uticaj mlevenja i odgrevanja legure Ni-11,3Fe-1,4W na električna i magnetna svojstva. Strukturne promene legure se odigravaju i tokom odgrevanja i tokom mlevenja. Odmah nakon deponovanja legura je zagrevana do 420ºC. Tokom zagrevanja došlo je do procesa strukturne relaksacije koja je uzrokovala smanjenje električne otpornosti i povećanje magnetne permeabilnosti legure. Daljim zagrevanjem legure na temperaturama višim od 4200C odvija se proces kristalizacije koji dovodi do smanjenja i električne otpornosti i magnetne permeabilnosti. Mlevenjem legure do 12 časova u leguri se u izvesnoj meri odvijaju i proces strukturne relaksacije i proces kristalizacije. Porast kristalnih zrna do 11 nm i delimična strukturna relaksacija uzrokuju smanjenje električne otpornosti i povećanje magnetne permeabilnosti legure. Zagrevanjem prahova dobijenih mlevenjem do 4200C dolazi do potpune strukturne relaksacije, smanjenja električne otpornosti i povećanje magnetne permeabilnosti. Tokom zagrevanja prahova dobijenih mlevenjem na temperaturama višim od 420ºC dolazi do kristalizacije i značajnog porasta veličine kristalnih zrna, a to dovodi do smanjenja i električne otpornosti i magnetne permeabilnosti. Najbolja magnetna svojstva imaju legure mlevene 12 časova, a zatim odgrejane na 420ºC. U ovim legurama kristalna zrna imaju optimalnu veličinu, a proces relaksacije se potpuno odigrao, što uzrokuje maksimalan porast magnetne permeabilnosti.