As-cast Ones Research Articles

2311 摩擦攪拌により組織改質した鋳造アルミニウム合金AC4CHの疲労挙動(S07-2 非鉄材料の疲労特性,S07 構造材料の疲労強度とき裂進展問題)

The fatigue behaviour of friction stir processed (FSPed) cast aluminium alloy, AC4CH-T6 was investigated. Fully reversed axial fatigue tests have been performed using as-cast, FSPed and post heat treated (PHTed) specimens. The FSPed specimens exhibited lower fatigue strength in high stress region, but higher fatigue limit than the as-cast specimens. Casting defects were eliminated by FSP, resulting in higher fatigue limit. However, the crack growth rates of the FSPed specimens were faster than the as-cast ones due softening of the material by heat input during FSP. This led to the lower fatigue strength of the FSPed specimens in high stress region. Post heat treatment could recover the hardness, but it was detrimental to crack initiation resistance. The effects of FSP and PHT were discussed based on the microstructural consideration.

Magnetostriction and electrical resistivity of Si doped Tb0.3Dy0.7Fe1.95 oriented crystals

Magnetostriction and the electrical resistivities of as-cast and ⟨110⟩ oriented crystals of Tb0.3Dy0.7(Fe1−xSix)1.95 (x=0,0.025,0.1) were investigated. Giant magnetostriction and obvious magnetostrictive jump effect were observed in oriented Si doped TbDyFeSi crystals especially for x=0.025. The electrical resistivities of both as-cast and ⟨110⟩ oriented TbDyFeSi were studied at the temperature range from 250to300K. Drastic increases of resistivity were observed in the as-cast Si doped TbDyFeSi magnetostrictive alloys with the increase ratios of 66% and 97% for x=0.025 and 0.1, respectively, compared with traditional Tb0.3Dy0.7Fe1.95 alloy. The electrical resistivities of oriented alloys are slightly smaller in comparison with that of the as-cast ones.

Surface segregational behaviour studied as an effect of thickness by SIMS and AFM in annealed PS-PMMA blend and block copolymer thin films

The surface behaviour of a two-phase polymer mixture depends on the chemical structure of the polymer components, the interaction between the two polymers and the processing conditions. The microscopic morphology and the surface composition need to be known in order to fully utilize the thin film properties. The technique of static time-of-flight secondary ion mass spectrometry (ToF-SIMS) is used to obtain the molecular surface composition of thin films of blends and block copolymers. The depth profiling tool of Nano-SIMS, a dynamic SIMS technique, helps to provide the chemical mapping of the surface in 2D and 3D. The surface morphology is investigated using AFM. Thin films of PS and PMMA diblock copolymers with molecular weight of 12K-12K and 10K-10K and blends of PS/PMMA (10K/10K) for thicknesses ranging from 5 nm to 50 nm are examined. For the blends, the ToF-SIMS spectra for all the thicknesses show the same behaviour of a high increase of PMMA on the surface after annealing. Nano-SIMS images reveal the formation of nanostructures on the annealed surfaces and AFM studies show these nanostructures to be droplets having distinct phase shift from the surrounding matrix. The droplet dimensions increase with the increase of the thickness of the film but the absolute intensity from the ToF-SIMS spectra for all the annealed films remains almost the same. For the copolymers, the ToF-SIMS spectra show that there is a decrease of PMMA on the surface for the annealed films when compared to the as-cast ones. AFM morphology reveals that, for different thicknesses, annealing induces different topographical features like droplets, holes, spinodal patterns, etc. but with no distinct phase shift between the patterns and the surrounding matrix. The two different copolymers of comparable molecular weight are found to exhibit very different topography even when the thickness of the films remained the same. The surface composition from the ToF-SIMS data, however, was not found to vary even when the topography was completely different.

Effect of carbon on microstructure and high-temperature strength of NbMoTiSi in situ composites prepared by arc-melting and directional solidification

Improvement of high-temperature strength of Nb–(10–20)Mo–22Ti–18Si alloys by adding carbon and directional solidification technique has been investigated. Vickers hardness HV and compressive strength at 1470 and 1670 K were examined. The as-cast specimen without C composes of Nb solid solution (Nb SS) and (Nb,Mo,Ti) 5Si 3 silicide, while (Nb,Ti)C carbide obviously appears when contain more than 2.4 mol% carbon. The amount of carbide and silicide phases increases with increasing carbon content. The directionally solidified samples have the same phases as the as-cast ones and show coarse microstructure slightly oriented to the direction of growth. A small amount of carbon addition lowers both the HV and strength at 1470 and 1670 K, where corresponds with the appearance of the carbide phase. By adding more than 4.8 mol% carbon, however, the HV, 0.2% yield strength ( σ 0.2) and maximum strength ( σ max) tend to increase. The directional solidification samples show higher strength and work hardening rate than the as-cast ones at corresponding C content. The 10 mol% Mo sample is weakened by C addition, but a considerable improvement in strength at elevated temperatures can be predicted when more than 10 mol% C is added to the 20 mol% Mo material. The sliding and debonding of the Nb SS/silicide interfaces is dominant in compressive damage at elevated temperatures.

Effect of microstructure on the sliding wear performance of a Zn–Al–Ni alloy

Some observations pertaining to the sliding wear characteristics of a zinc–aluminium alloy containing nickel under varying material and test conditions have been reported in this investigation. Dry sliding wear tests were conducted on as-cast and heat-treated zinc-based alloy pins using a pin-on-disc machine. A steel disc was employed as the counterface. Sliding speeds adopted were 0.42, 2.68 and 4.60 m/s while the traversal distance was fixed at 500 m. Wear tests were conducted at different pressures using separate pins in each case. Seizure pressure of the pins (prior to traversing the sliding distance of 500 m) was determined at each speed. Wear rate and the extent of frictional heating increased with pressure and speed whereas seizure pressure practically followed a reverse trend. The wear rate versus pressure plot of the as-cast alloy pins assumed two slopes at the lowest speed wherein low slope (indicating the occurrence of mild wear situation) was noticed initially. This was followed by the attainment of a higher slope suggesting severe wear condition at increased pressures. At higher speeds, one slope only (identical to the higher slope at the minimum speed) was noted. Wear rate versus pressure plots of the heat-treated alloy pins followed a trend similar to the as-cast ones except that two slopes were noted up to the intermediate speed in the former case. Heat treatment changed the as-cast dendritic structure of the zinc-based alloy into the one with an improved uniformity of the distribution of various microconstituents, the nickel containing phase remaining practically unaffected. Softening of the (as-cast) alloy was also observed as a result of the heat treatment. However, in spite of reduced hardness, the heat-treated alloy pins attained improved wear behaviour (i.e. reduced frictional heating and low wear rate) over the as-cast ones irrespective of the test conditions. This was attributed to a more uniform distribution of microconstituents and reduced cracking tendency of the alloy as a result of the heat treatment. The alloy pins also attained better seizure pressure in heat-treated condition comparing with the as-cast ones at all the speeds except the maximum for the same reasons. A reversal in the trend at the maximum speed was thought to be due to the over-softening of the already softened (heat-treated) alloy pins under the influence of large frictional heat generated at the (maximum) speed. Under the circumstances, the heat-treated alloy pins tended to adhere/fuse with the disc extensively while this tendency was relatively less for the as-cast ones in view of their higher hardness. Further, the extent of the negative influence of cracking tendency reduced allowing thermal stability to predominate the wear behaviour of the as-cast alloy pins in this case. The factor led to somewhat higher seizure pressure of the (as-cast) alloy pins at the maximum speed comparing with the heat-treated ones. Low wear rates correlated with less damage to the worn surfaces and to the regions below the worn surfaces and finer debris formation. Seizure led to severe damage to the worn surfaces and to the regions below the worn surfaces while the debris formed was quite bulky and coarser.

Effect of Hot Rolling on the Microstructure and Mechanical Properties of Ti3Al Based Dual Phase Alloys

ABSTRACTDevelopment of α2-Ti3A1 based dual phase alloys have shown some promising potentials in property improvement by introducing Ti5Si3sulicide phase into the matrix via Si alloying. However, the presence of coarse network of Ti5Si3phase formed by eutectic reaction in the as-cast state also embrittles the alloy. Both hot rolling and powder metallurgy are considered to be the possible ways to refine the Ti5Si3phase in the matrix. Two Ti-Al-Si-Nb alloys whose Si contents are 2 and 5 at. % respectively were arc melted into ingots and then hot rolled to sheets in this investigation. Optical metallographic examination correlates the microstructures of the as-cast and as-rolled alloys with the different rolling amounts, showing that the coarse silicide network is broken into small particles after hot rolling. Mechanical property testing from room temperature to 8000°C indicates that the strength and plastic elongation of the hot-rolled alloys are much higher than those of the as-cast ones. The data obtained in this investigation are comparable with those obtained in the P/M processed specimens. Fracture surfaces of the alloys are also examined.

Different mechanism of induced helical anisotropy in low-magnetostriction amorphous ribbons

Magnetization processes with large Barkhausen jumps can be obtained in low-magnetostrictive amorphous ribbons with helical induced anisotropy. In this work, we have made a study of the induction of such anisotropies showing that in as-cast samples stronger anisotropies can be induced than in samples pre-annealed above the Curie temperature. The kinetics of the anisotropy induction is faster in pre-annealed samples than in as-cast ones. On the other hand, the existence of a previous anisotropy slows the kinetics of the induction of the helical anisotropy.

マイカ系キャスタブル・セラミックス（ＯＣＣ）・クラウンの寸法精度に関する研究

This article discussed the dimensional accuracy of Olympus Castable Ceramics (OCC) crowns at the stage of as-cast and crystallization. The master die technique and three coordinate measuring method were used for their measurement. Moreover, the surface roughness of inner crowns were measured and following results were obtained.1. OCC crowns, heat-treated at 850°C were rather expanded than at 900°C or 950°C in the master die technique. But the differences between at 900°C and 950°C were not significant.2. In the master die technique, each crown fabricated with special investment liquid, which was diluted with 25%, 50% and 75% distilled water showed expansional ratios of 0.35%, -0.23%and -0.86%, respectively.3. In the master die technique, buffering factors, ringless, one fold of liner and two folds of liner did not affect the expansional ratio.4. In three-coordinate measuring, each diameter of as-cast crowns expanded equally in the range of 1.0-7.0mm from occlusal plane. But, 9.0mm near the cervical portion expanded less than the others.5. In three-coordinate measuring, about 0.70-0.81% shrinkage were founded at the inner diameter of crystallized crowns.6. In measuring for surface roughness of inner crowns, crystallized crowns were roughened more than as-cast ones in both of Ra and Rmax.