• Transactions of Materials Processing
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• v.32 no.4
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• pp.173-179
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• 2023

In this study, the age-hardening behavior and tensile properties of a cast AZ91-0.3Ca-0.2Y (SEN9) alloy are investigated and compared with those of a commercial AZ91 alloy. Even after homogenization heat treatment, the SEN9 alloy contains numerous undissolved secondary phases, Al₈Mn₄Y, Al₂Y, and Al₂Ca, which results in a higher hardness value than the homogenized AZ91 alloy. Under aging condition at 200 ℃, both the AZ91 and SEN9 alloys exhibit the same peak-aging time of 8 h, but the peak hardness of the latter (86.8 Hv) is higher than that of the former (83.9 Hv). The precipitation behavior of Mg₁₇Al₁₂ phase during aging significantly differs in the two alloys. In the AZ91 alloy, the area fraction of Mg₁₇Al₁₂ discontinuous precipitates (DPs) increases up to ~50% as the aging time increases. In contrast, in the SEN9 alloy, the formation and growth of DPs during aging are substantially suppressed by the Ca- or Y-containing particles, which leads to the formation of only a small amount of DPs with an area fraction of ~4% after peak aging. Moreover, the size and interparticle spacing of Mg₁₇Al₁₂ precipitates of the peak-aged SEN9 alloy are smaller than those of the peak-aged AZ91 alloy. The homogenized AZ91 alloy exhibits a higher tensile strength than the homogenized SEN9 alloy due to the finer grains of the former. However, the peak-aged SEN9 alloy has a higher tensile elongation than the peak-aged AZ91 alloy due to the smaller amount of brittle DPs in the former.

• The Journal of Korean Academy of Prosthodontics
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• v.41 no.1
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• pp.1-19
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• 2003

The surface of metals should be as smooth as possible for optimum comfort, oral hygiene, low plaque retention, and resistance to corrosion. In this study five specimens of each precious metal(type III gold alloy, ceramic gold alloy, and Ag-Pd alloy) were divided into five groups according to finishing and polishing procedures : group 1(sandblaster), group 2(group 1+stone), group 3(group 2+brown rubber), group 4(group 3+green rubber), and group 5(group 4+rouge). Six specimens of each non-precious metal(Co-Cr alloy, Ni-Cr alloy, and Co-Cr-Ti alloy) were divided into six groups: group 1(sandblaster), group 2(group 1+hard stone), group 3(group 2+electrolytic polisher), group 4(group 3+brown hard rubber point), group 5(group 4+green hard rubber point), and group 6(group 5+rouge). Considering factors affecting the rate of abrasion, the same dentist applied each finishing and polishing procedure. In addition, the surface roughness of enamel, resin, and porcelain was evaluated. The effect of finishing and polishing procedures on surface roughness of precious and non-precious metals, enamel, resin, and porcelain was evaluated by means of Atomic Force Microscope(AutoProbe CP. Park Scientific Instruments, U.S.A.) that can image the three dimensional surface profile and measure average surface roughness values of each sample at the same time. The obtained results were as follows : 1. According to finishing and polishing procedures, the surface roughness of type III gold alloy, ceramic gold alloy, and Ag-Pd alloy was decreased in the order of group 1, 2, 3, 4, and 5 (P<0.01). 2. According to finishing and polishing procedures. the surface roughness of Co-Cr alloy, Ni-Cr alloy, and Co-Cr-Ti alloy was decreased in the order of group 1, 2, 3, 4, 5, and 6 (p<0.01). 3. There was not statistically significant difference in the surface roughness among three metals of precious metals in group 1 but was significant difference in group 2, 3, 4, and 5 (P<0.05). 4. There was not statistically significant difference in the surface roughness among three metals of non-precious metals in all groups. 5. When the surface roughness of the smoothest surface of each metal, enamel. porcelain, and resin was compared, porcelain was the smoothest and the surface roughness was decreased in the order of Ni-Cr alloy. Co-Cr alloy. Co-Cr-Ti alloy, resin. Ag-Pd alloy, ceramic gold alloy type III gold alloy, and enamel (P<0.01). The results of this study indicate that the finishing and polishing procedures should be carried out in a logical, systematic sequence of steps and the harder non-precious metals may be less resistance to abrasion than are the softer precious metals.

• The Journal of Advanced Prosthodontics
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• v.6 no.5
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• pp.372-378
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• 2014

PURPOSE. The porcelain fused to gold has been widely used as a restoration both with the natural esthetics of the porcelain and durability and marginal fit of metal casting. However, recently, due to the continuous rise in the price of gold, an interest towards materials to replace gold alloy is getting higher. This study compared the bond strength of porcelain to millingable palladium-silver (Pd-Ag) alloy, with that of 3 conventionally used metal-ceramic alloys. MATERIALS AND METHODS. Four types of metal-ceramic alloys, castable nonprecious nickel-chrome alloy, castable precious metal alloys containing 83% and 32% of gold, and millingable Pd-Ag alloy were used to make metal specimens (n=40). And porcelain was applied on the center area of metal specimen. Three-point bending test was performed with universal testing machine. The bond strength data were analyzed with a one-way ANOVA and post hoc Scheffe's tests (${\alpha}=.05$). RESULTS. The 3-point bending test showed the strongest ($40.42{\pm}5.72$ MPa) metal-ceramic bond in the nonprecious Ni-Cr alloy, followed by millingable Pd-Ag alloy ($37.71{\pm}2.46$ MPa), precious metal alloy containing 83% of gold ($35.89{\pm}1.93$ MPa), and precious metal alloy containing 32% of gold ($34.59{\pm}2.63$ MPa). Nonprecious Ni-Cr alloy and precious metal alloy containing 32% of gold showed significant difference (P<.05). CONCLUSION. The type of metal-ceramic alloys affects the bond strength of porcelain. Every metal-ceramic alloy used in this study showed clinically applicable bond strength with porcelain (25 MPa).

• Journal of the Korean institute of surface engineering
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• v.51 no.3
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• pp.139-148
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• 2018

In this study, surface analysis of Ni-Cr and Co-Cr alloys with addition of Ti and Mo for dental CAD/CAM use has been researched experimentally. The surface characteristics of the alloys were examined by Vickers hardness test, bonding strength test, surface roughness test, field-emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction spectroscopy. The shrinkage of the sintered Ni-Cr alloy alloy was slightly larger than that of Ni-Cr-Ti alloy, and larger than Co-Cr alloy. Also, the addition of Mo showed a tendency to decrease shrinkage somewhat. From the result of XRD analysis, NiCr, $Ni_3Cr$ and $Ni_3Ti$ were observed in the sintered Ni-13Cr-xTi and Ni-13Cr-xMo alloys. In addition, ${\sigma}-CrCo$, $Co_2Mo_3$ and $TiCo_2$ were formed in the sintered Co-Cr-xTi and Co-Cr-xMo alloys. Surface hardness of Ti and Mo added alloy was higher than those of Ni-Cr and Co-Cr alloy. The bond strength between sintered alloy and porcelain was $16.1kgf/mm^2$ for Ni-13Cr alloy, $17.8kgf/mm^2$ for Ni-13Cr-5Ti alloy, and $8.2kgf/mm^2$ for Ni-13Cr-10Ti alloy, respectively.

• Journal of Technologic Dentistry
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• v.35 no.2
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• pp.113-120
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• 2013

Purpose: This study was to observe surface property and bonding strength according to composition of Ni-Cr alloy for porcelain fused to metal crown. The two kinds of Ni-Cr alloy with different composition ratio of parent metal were observed general properties and chemical properties of each alloy surface and measured the shear bonding strength between ceramic and each alloys. The aim of study was to suggest the material for design of parent metal's composition ratio to development of alloy for porcelain fused to metal crown. Methods: The two kinds of alloy as test specimen was Ni(71wt.%)-Cr(12wt.%) and Ni(63wt.%)-Cr(23wt.%) alloy. The oxide on surface was observed by SEM and EDX. And the shear test was performed by MTS. Results: The surface property and oxide characteristic analysis of oxide layer, weight percentage of Element O within $Ni_{71}Cr_{12}$ alloy measured 12.74wt.%, but $Ni_{63}Cr_{23}$ alloy was measured 15.91wt.%. And the maximum shear bonding strength was measured 106.14MPa between $Ni_{71}Cr_{12}$ alloy and vintage halo (VV group). Conclusion: The surface property and oxide characteristic of $Ni_{71}Cr_{12}$ alloy was similar to $Ni_{63}Cr_{23}$ alloy. And VV group has the strongest shear bonding strength.

• The Journal of Korean Academy of Prosthodontics
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• v.27 no.1
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• pp.143-179
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• 1989

To observe the bonding behavior of palladium-based alloys to porcelain; 1. Pd-Co binary alloy with the higher cobalt content, 2. Pd-Co binary alloy with the lower cobalt content, 3. Pd-Ag-Sn ternary alloy, 4. Pd-Ag binary alloy, 5. Pd-Cu-Au ternary alloy and 6. Pd-Cu binary alloy were made as 6 groups of experimental alloys. Each group of alloy was divided into 4 sub-groups such as one sub-group that was not degassed and three sub-groups that degassed for 5 minutes, 10 minutes and 15 minutes. On each specimen, weight changes after degassing, morphological changes of oxide layer by changing the degassing time, compositional changes at metal-ceramic interface and bond strength of metal-ceramic measured with planar shear test were observed and compared. The results of the present study allow the following conclusions to be drawn: 1. The alloy showing the greatest bond strength was Pd-Cu alloy without gold and bond strength was decreased by alloying gold to them. 2. Although Pd-Co alloy showed the most prominent oxidation behavior, bond strength of them to porcelain was not greatly high by the formation of porosities at metal-ceramic interfaces. 3. Likewise tin, cobalt formed the peaks on line profiles at metal-ceramic interface, however copper did not exhibit such peaks on line profiles. 4. Mainly, oxide layer on Pd-Co alloy was composed with cobalt, and for Pd-Co alloy with higher cobalt content the rise of bond strength was not significant by increased degassing time. 5. On Pd-Ag alloy not containing tin, during degassing for 15 minutes silver content was increased at metal-ceramic interface. 6. As an oxidized element, tin formed the oxide layers that widen their area by increasing the degassing time, while cobalt and copper showed the morphological changes of particle or crystal on oxide layer.

• The Journal of Korean Academy of Prosthodontics
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• v.34 no.3
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• pp.475-488
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• 1996

The opaque porcelain layer of porcelain-fused-to-metal(PFM) restoration is critical for the success of PFM restoration because it is the first layer placed over the treated alloy. But, the methods of opaquing technique have not been confirmed. Usually, the one layer method and two layer method have been used for the application of opaque porcelain. In the past, alloys with porcelain veneers which have been used successfully have contained various precious metals. Recent increase in the cost of precious metals stimulates considerable interest in nonprecious alloys. Although nickel-chromium alloys and nickel-chromium-beryllium alloys have been widely used, the use of cobalt-chromium alloys would be gradually increased with elimination of any potential risk of nickel-related allergic responses and/or beryllium-related toxic responses. This investigation examined one- and two-layer opaque porcelain applications to determine the effect on the bond strength of titanium added cobalt-chromium metal ceramic alloy. Bond strength of Ceramco II porcelain to titanium added cobalt-chromium alloy(2Dentitan) and gold-platinum-palladium alloy(Degudent H) were evaluated by direct shear bond strength test with Instron universal testing machine. The results were as follows; 1. When the mean shear bond strength of each experimental group were compared in $0.25cm^2$ unit area, the titanium added cobalt-chromium alloy/two layer method exhibited the greatest strength(79.7kg), followed by titanium added cobalt-chromium alloy/one layer method(76.2kg), gold-platinum-palladium alloy/two layer method(71.4kg), gold-platinum-palladium alloy/one layer method(64.2kg). 2. No significant differences in bond strength were recorded between the two opaquing techniques for gold-platinum-palladium alloy and titanium added cobalt-chromium alloy. 3. No significant differences in bond strength were recorded between the gold-platinum-palladium alloy and the titanium added cobalt-chromium alloy.

• Journal of Korea Foundry Society
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• v.38 no.6
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• pp.121-131
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• 2018

The effect of additives on the castability of the AC2BS aluminum alloy, which contains 35% recycled scrap, was investigated. For the wide utilization of the recycled scrap AC2BS aluminum alloy, the research results were compared to those with the AC2B virgin alloy, which is typical Al-Si-Cu alloy system. It was confirmed that the addition of Al-5%Ti-1%B increased the ${\alpha}$-Al nucleation temperature during solidification and decreased the grain size through cooling curve and microstructural observations of the recycled alloy. It was also found that an addition of Al-10%Sr decreased the eutectic Si growth temperature during the solidification process and modified the shape of the eutectic Si of the recycled alloy. The characteristics of fluidity, shrinkage and solidification crack strength were evaluated. For the AC2BS aluminum alloy containing 35% recycled scrap, both ${\alpha}$-Al grain refinement due to Ti-B and eutectic Si modifications due to Sr contributed to the improvement of the fluidity. The macro- shrinkage ratio increased with additions of both Al-10%Sr and Al-5%Ti-1%B and the micro-shrinkage ratio increased with the addition of Al-10%Sr but decreased with the addition of Al-5%Ti-1%B. The casting characteristics of TiB and Sr-treated AC2BS aluminum alloy containing 35% recycled scrap are similar to those of AC2B virgin alloy. The improvement of the solidification crack strength of the AC2BS aluminum alloy was possible by the reduction of the grain boundary the stress concentration through the enhancement by both ${\bullet}{\cdot}$-Al refinement and eutectic Si modification. More extensive use of the AC2BS aluminum alloy containing 35% recycled scrap can be expected in the future.

• The Journal of Korean Academy of Prosthodontics
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• v.34 no.1
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• pp.125-142
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• 1996

Bond strength of four different cements to dental casting alloys which were treated with #600 emery, tin-plating, and $50{\mu}m$ sandblasting were evaluated. The alloy specimens were Type III Gold alloy(Degulor C), Palladium-Silver alloy(Pors on 4), Nickel-Chromium(Rexillium III) alloy, which were embedded in acrylic resin disc. The specimens were treated with #600 emery and tin plating, #600 emery and sandblasting, then bonded using Fuji I, Ketac Cem(Glass ionomer cements), Poly F, Livcarbo(Polycarboxylate cements). The specimens were immersed in water for 24 hours and shear bond strengths were evaluated by Instron Machine. Tin plated, sandblasted, and debonded alloy surfaces were observed using scanning electron microscope. On the basis of this study, the following conclusions could be drawn. 1. In the tin plated alloy group, increase in bond strength of glass ionomer cements was statistically insignificant. 2. In the tin plated alloy group, increase in bond strength of polycarboxylate cements was statistically significant, except nickel-chromium alloy. 3. Sandblasted alloy group showed higher bond strength than that of tin-plated alloy group.

• Journal of Powder Materials
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• v.16 no.4
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• pp.275-279
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• 2009

The aging characteristics of gas atomized Mg-6 wt.% Al-1 wt.% Zn alloy were investigated and compared to those of cast Mg-6 wt.% Al alloy. The gas atomized Mg-6 wt.% Al-1wt.% Zn alloy powders had spherical morphology between 1 and 100 $\mu m$ in diameter. After compaction under the pressure of 700 MPa at $320^{\circ}C$ for 10 min, the Mg-6 wt.% Al-1 wt.% Zn alloy showed a grain size of approximately 40 $\mu m$ which is smaller than that of the cast Mg-6 wt.% Al alloy, and a relative compact density of approximately 93%. After ageing, the Mg-6 wt.% Al-1 wt.% Zn alloy showed much faster peak hardness than cast Mg-6 wt.% Al alloy. The Mg-6 wt.% Al-1 wt.% Zn alloy showed the new fine precipitations with ageing time, while the cast Mg-6 wt.% Al alloy was almost similar morphology.