발간논문

Home > KJMM 논문 > 발간논문

Effects of sputtering conditions and rotating field annealing(RFA) on magnetic properties of CoNbZr thin films were studied. With increasing Ar pressure from 0.5 to 10 coercivity showed constant value until 5mTorr, then increased at the higher pressure. Co_(90.1)Nb_(6.7)Zr_(3.2)filM of 0.3㎛ thick showed 4 πMs of 11.5 kGauss, curies temperature of 540℃ and crystallizetion temperature of 520℃, and thess values did not change with sputtering parameters and RFA. Magnetic properties of as-asputtered films with and without applied external during sputtering showed significant differences. However, those differences were greatly reduced as the following RFA temperatures increased. The origin of coercivity was considered to be affributed to magnetostricition in this film.

keyword :

The effect of heat treatment condition on the martensitic transformation behavior and shape memory effect in Fe-15Mn-5Cr-5Co-3Si alloy has been studied by microscopy and calorimetry. The grain size increased with the increase in heat treatment temperature and holding time. Three types of transformation behavior, such as no martensitic transformation, r→ε and r→ε→α` were observed in increasing order of grain size. The r phase did not seem to transform directly to α`, for α` martensite was found only in the a martensite plates. The orientation relationships between the ε and the α` martensites were [011] ε∥ [311]α`, (1￣00) ε∥ (1￣12) α` and [011] ε∥ [111] α`, (1￣11￣) ε ∥ (1￣01) α`. The Ms temperature of r→ε transformation remained almost constant, while that of ε→α` transformation increased rapidly with the increase in grain size. As the heat treatment temperature and holding time increased, the shape memory effect became worse. This could be attributed to the reduction of r phase contributing to the shape memory effect and the easiness of movement of dislocations during the deformation.

keyword :

The dissolution of silver in NH₄SCN solution containing Fe^(+3) ion and O₂ gas as an oxidant was studied. It was found that the dissolution rate was effected by a pH of solution, concentration of NH₄SCN, O₂ gao and Fe^(+3)ion. And also a transition from diffusion control to chemical reaction control has been noted at a reaction temperature of 60℃.

keyword :

One aspect of the properties of austempered ductile iron (ADI) which should be exploited further in promoting engineering applications is their fracture toughness. In this study ductile irons with various Si content were austempered and the relationship among austempering temperatures, quantity of retained austenite and fracture characteristics was investigated. As Si content increases from 2.28% to 3.0%, the precipitation of carbide during bainite transformation is suppressed, and the fracture toughness and the amount of the retained austenite is increased. The high Si content limits the formation of martensite in the structure and minimizes segregation of other elements at cell boundaries. But in the excessive Si content (3.3%) showed the formation of islands of free ferrite in the bainitic structures and it decreased the fracture characteristics.

keyword :

In this study, continuous casting of titanium and TiAl intermetallic compound was performed by the PAM(plasma arc melting) process. In the PAM process, a water cooled copper mould was used for the prevention of crucible reaction with titanium melt. The effects of Ar gas pressure, remelting and continuous casting speed on the oxide formation and microstructure of titanium ingots were studied. Titanium ingot produced by continuous casting speed of 2.0㎝/min. has more porosity than that of 1.5㎝/min. The increase in Ar gas pressure in melting chamber reduced the evaporation of aluminum during continuous casting. Remelting in continuous casting was found to minimize porosity and to increase alloy uniformity. Proper control of the process parameters such as mold temperature gradient, continuous casting speed and Ar gas pressure in the melting chamber is necessary in order to fabricate sound ingots by the PAM process.

keyword :