The objective of this work was to study the effect of different heating-up procedures and isothermal treatment times on crystallization, densification and properties of a sintered non-stoichiometric ...lithium silicate glass-ceramic. Glass samples containing SiO2, Li2O and K2O as main constituents, besides minor amounts of other oxides such as Al2O3, P2O5 and ZrO2, were melted at 1500 °C - 60 min and subsequently fragmented (<25 μm) into a fine powder. The obtained glass particles were characterized by scanning electron microscopy SEM, X-ray diffraction, XRD and differential thermal analysis, DSC. The thermal analysis indicated the presence of two exothermal peaks, the first at approximately 640 °C, characteristic of the crystallization of lithium metasilicate, Li2SiO3, and the second close to 820 °C, corresponding to the crystallization of lithium dissilicate, Li2Si2O5. In order to study the crystallization behavior the glass powder was uniaxially compacted and investigated by dilatometry. The samples were sintered under different conditions: Group 1: sintering at 840 °C with isothermal holding times of 5, 15, 60 and 180 min; Group 2: preheating to 660 °C with an isothermal plateau for 720 min and further heating up to 840 °C with identical holding times of 5, 15, 60 and 180 min. The sintered glass-ceramics were characterized by XRD, Rietveld refinement, SEM, relative density, hardness, fracture toughness and flexural strength. The results showed that the samples of group 1, directly heated up to 840 °C, achieved a relative density ranging between 60 and 70% and a hardness and fracture toughness lower than the second group that was subjected to a differentiated preheating process. The sintered samples for less than 60 min, presented Li2SiO3 and Li2Si2O5 as crystal phases and a microstructure formed by low aspect ratio crystals, besides apparent porosity. The samples sintered at 840 °C for 180 min, independently of the heating up procedure, presented only Li2Si2O5 as crystal phase with elongated grains with an aspect ratio higher than 2 and relative densities in the order of 84 to 91%. The hardness ranged in the order of 5.6 to 6 GPa and the average fracture toughness was 1.5 MPa m1/2. The materials subjected to the preheating process and treated at 840 °C for 180 min exhibited a flexural strength of 160 MPa, while those directly heated to 840 °C and treated for 180 min showed a flexural strength of only 75 MPa.
Vickers indentation (IF) and single‐edge‐V‐notched beam (SEVNB), to measure the fracture toughness (KIC) of zirconia‐based dental ceramics and mathematical models were proposed to establish a ...correlation between both. Zirconia (ZrO2) stabilized with 3 mol. % of Y2O3 (3Y‐TZP) and 5 mol% of Y2O3 (5Y‐PSZ) were compacted (n = 42) and sintered for 2 h at different temperatures (1475°C, 1500°C, 1550°C, or 1600°C). After sintering, they were characterized by relative density using the ASTM C373‐88 standard, X‐ray diffraction (XRD) and scanning electron microscopy (SEM). The average grain size was measured according to the ASTM E1382‐97 standard. The fracture toughness (KIC) was determined using two methods: Vickers indentation fracture toughness (KIC‐IF): method based on mathematical modeling that considers the parameters used for the Vickers hardness test and Fracture toughness by the single‐edge‐V‐notch‐beam (KIC‐SEVNB): method proposed by ISO 23146:08. The main phases of the 3Y‐TZP and 5Y‐PSZ ceramics were ZrO2‐tetragonal and ZrO2‐cubic, respectively. The 3Y‐TZP specimens showed equiaxed grains with average grain sizes ranging from 0.55 to 0.79 μm. The grain sizes of 5Y‐PSZ of specimens sintered at 1475°C and 1600°C were 0.62 and 2.32 μm, respectively. For all ceramics the crack size ratio was c/a < 2.5, suggesting a Palmqvist‐type crack system. The fracture toughness measured by the Vickers indentation method (KIC‐IF) and by the SEVNB method (KIC‐SEVNB) was the same when the experimental data were fit to a mathematical model.
In this work, three different commercial lithium silicate (LS) glass‐ceramics for computer aided design/computer aided machining systems, CeltraDuo‐Dentsply (LS‐C), E‐MaxCAD‐Ivoclar (LS‐E), and ...Suprinity‐Vita (LS‐S), were comparatively characterized. Following the protocols recommended by the manufacturers, the glass‐ceramics were heat‐treated under low vacuum and characterized by X‐ray diffraction, scanning electron microscopy, hardness, fracture toughness, Young's modulus, and flexural strength. Rietveld refinement indicated that the materials “as‐received” present mostly amorphous phase and Li2SiO3 as secondary crystalline phase in LS‐E and LS‐S specimens, while LS‐C specimens also present Li2Si2O5 and Li3PO4 as crystalline phases. All “as‐received” glass‐ceramics present hardness, fracture toughness, and Young's modulus of around 647‐678 HV, 1.15‐1.40 MPa.m1/2, and 82‐92 GPa, respectively. After heat treatment, the LS‐C and LS‐S specimens presented decreasing of amorphous phase associated to Li2SiO3 and Li2Si2O5 grains with low aspect ratio, while LS‐E indicates a reduction of amorphous phase and Li2Si2O5 elongated grains. Fracture toughness and Young's modulus increase about 10% due to the crystallization of residual amorphous phase for all materials. Moreover, crystallographic and microstructural characteristics are responsible for the higher flexural strength of LS‐E (327 MPa), regarding LS‐C and LS‐S. However, the glass‐ceramics LS‐E present lower Weibull modulus (m = 5.4) comparatively to LS‐C (m = 9) and LS‐S (m = 6).
The objective of this work was the development and characterization of a ceramic composite based on (Ce,Y)-TZP/Al2O3 aiming an application on dental implants, comparing it with conventional ...monolithic 3Y-TZP ceramics, currently used for the same type of application.
Ceramic samples, 3Y-TZP (n = 40) and (Ce,Y)-TZP/Al2O3 (n = 40), were sintered at 1500 °C - 2h and characterized by relative density, X-Ray diffraction (XRD) and microstructure. Then, the samples of both materials were divided into two groups: 1) samples with original (as sintered) surfaces; 2) samples with conditioned, polished, surfaces. All samples were submitted to hydrothermal degradation tests, on an autoclave (134 °C - 2 bar), for 10 h in artificial saliva. The degraded samples were characterized by XRD and the polished group were also characterized by their elastic moduli, Vickers hardness and fracture toughness (Vickers indentation method). Both groups were also submitted to a flexural strength test, 3B–P testing, for which the data were interpreted using Weibull statistics.
All sintered specimens presented nearly full densification. After the hydrothermal degradation tests, 3Y-TZP samples presented 16.4% of monoclinic (m)-ZrO2 phase while the composite samples withheld 100% of tetragonal (t)-ZrO2 phase. Both materials presented equiaxial ZrO2 grains with an average size of 0.48 ± 0.17 μm and 0.75 ± 0.22 μm, respectively, for the monolithic and composite ceramics. In the composites, is observed the presence of well distributed Al2O3 grains on the ZrO2 matrix, in two distinct morphologies: equiaxial grains and platelets. The composites (Ce,Y)-TZP/Al2O3 presented average values of elastic moduli, Vickers hardness and fracture toughness of 228.3 ± 6.5 GPa, 1427 ± 46 HV e 11.3 ± 0.4 MPa m1/2, respectively. An inversely proportional relationship is observed between the roughness and the bending strength, since the 3Y-TZP samples presented a average strength of 860.7 ± 81 MPa (as-sintered) and 965.4 ± 93 MPa (polished) while the (Ce,Y)-TZP/Al2O3 composites presented average strength of 810.6 ± 147 MPa (as-sintered) and 952.6 ± 88 MPa (polished).
The composites (Ce,Y)-TZP/Al2O3 showed high resistance to degradation in saliva and adequate properties for use as dental implants. Values of flexural strength (>950 MPa) and Weibull modulus (m > 10) were similar to the conventional 3Y-TZP ceramics. Moreover, its hardness, elastic modulus and fracture toughness were higher than those obtained for 3Y-TZP. The expressive values of KIC obtained for (Ce,Y)-TZP/Al2O3 composites are results of association of different toughening mechanisms acting simultaneously in the material.
The effects of different surface finishing procedures on the translucency of yttria stabilized zirconia ceramics (ZrO2) were evaluated. ZrO2-3mol.%Y2O3 (designed Zr3) or ZrO2-5mol.%Y2O3(Zr5) ...specimens with thickness varying between 0.5 and 1.5 mm were obtained by sintering at 1500 °C for 2 h. Surface finishing of the sintered specimens was done in three distinct manners: polishing with diamond pastes, blasting with Al2O3 particles and blasting with Al2O3–SiO2 particles, according to the preparation protocol for dental prostheses. These sample groups were characterized by X-Ray diffraction analysis, scanning electron microscopy, surface roughness and spectrophotometry. The sintered ceramics exhibited relative densities higher than 99% and were composed of 68.5% and 31.5%of tetragonal (t)-ZrO2 and cubic(c)-ZrO2 for composition Zr3 and 25.2% and 74.8% for composition Zr5, respectively. Furthermore, 1.5 to 1.8% of monoclinic (m)-ZrO2, has been found in the blasted surfaces. The average grain size varied from 0.5 μm for Zr3 to 1.45 μm for the Zr5 samples. After polishing, all samples presented a surface roughness Raof about 0.05 μm, while blasting resulted in an increased roughness ranging between 1.24 μm and 1.49 μm.Samples rich in (c)-ZrO2 phase (Zr5) are more translucent than samples rich in (t)-ZrO2 (Zr3) because of their larger grain size and because the cubic phase is less anisotropic than (t)-ZrO2. Furthermore, the translucency of thinner samples is more affected by abrasive blasting because they also present the highly anisotropic monoclinic(m)-ZrO2 phase and, therefore, the reduction of translucency is more pronounced. Parameters such as grain size, crystalline phase composition, porosity and grain boundary density are used to explain the phenomena involved in the differences of translucency of these materials.
This work investigated the effect of a composite of tetragonal zirconia with alumina-reinforced Ceria (ATZ) previously synthesized, on the properties of alumina-based ceramics (Al2O3 ). Monolithic ...alumina powder and Al2O3 powder mixtures containing 5, 10, 15 and 20 wt.% of Ce-TZP/Al2O3 were processed by high energy milling, compacted and then sintered at 1600 °C - 2 h. Sintered pure alumina and composites were characterized by relative density, scanning electron microscopy, X-ray diffraction and surface roughness. Then, the elastic modulus, the Vickers hardness, the fracture toughness and the 4-point flexural strength were evaluated. The results indicated an increase in relative density as a function of the addition of ATZ, with values between 94.3 ± 0.8% and 98.9 ± 0.7%. The observed microstructure after sintering showed tetragonal ZrO2 grains with average sizes of 0.6 μm well dispersed in the Al2O3 matrix, which presents average grain sizes of around 1.5 μm. The crystalline phases identified in the composites were ZrO2-tetragonal and Al2O3 hexagonal. The addition of the composite (ATZ) in the alumina matrix generates a gradual reduction in the elastic modulus (398 ± 15 GPa ~366 ± 34 GPa) and in the hardness (20.5 ± 1 GPa ~17.3 ± 0.7 GPa) of the sintered ceramics. On the other hand, the addition of this same composite (ATZ) in the alumina matrix considerably increases the materials fracture toughness, reaching values of approximately 6.7 ± 0.9 MPa.m1/2. The same trend was observed in the flexural strength results which ranged from 258 MPa (5wt.% Ce-TZP/Al2O3 ) to 316 MPa (20wt.% Ce,Y-TZP/Al2O3 ). The Ce-TZP reinforcement acts as a toughening agent of the Al2O3 matrix due to the coupled mechanisms of toughening by zirconia phase transformation, residual stresses due to the difference in thermal expansion of the crystalline phases and differences in microstructural morphologies.
In this work, the effect of wear of diamond tools on the surface roughness and its influence on the mechanical properties of dental lithium silicate glass–ceramic milled by a CAD/CAM system was ...investigated. Cutting tools with distinct tool life, new cutting tool (NCT), mid-life cutting tool (MLCT) corresponding to cumulative 2 h of milling and end-of-life cutting tool (ELCT) corresponding to cumulative 4 h of milling were used for machining commercial lithium metasilicate LM, Li
2
SiO
3
, using a Sirona inLab MC X5
®
milling machine. The different tools were characterized by scanning electron microscopy (SEM). Their microstructure indicated a depletion of diamond particles on the surface, as a function of the accumulated time of use. The lithium metasilicate samples were characterized by their phase composition using X-ray diffraction (XRD) analysis and their microstructure by (SEM). Furthermore, the mechanical properties Vickers hardness, fracture toughness and the elastic parameters were determined. The as-received LM samples presented 44% of Li
2
SiO
3
and 56% amorphous phase. These LM samples exhibited a Vickers hardness of 6.1 ± 0.3 GPa, a fracture toughness of 1.3 ± 0.2 MPa m
1/2
, a modulus of elasticity of 82.3 GPa and a Poisson’s ratio of 0.16. The surface roughness of the machined LM samples was evaluated using a roughness meter. The profilometry measurements of the machined LM samples indicate a slight increase in the roughness parameter
R
a
with increasing wear of the cutting tools, i.e., using NCT, MLCT or ELCT tools, in addition to a considerable increase in the total height of the
R
t
profile from 11 to 17 µm. The formation of small microcracks during machining may nucleate new flaws in the material, if the critical initial crack size is exceeded. Aspects related to the performance of heat treatments for crystallization of lithium disilicate, Li
2
Si
2
O
5
, and its implications on the microstructure, softening of the residual amorphous phase and its surface roughness are discussed.
This work reports on effect of zinc and milling time on microstructure and Vickers hardness of mechanically alloyed and spark plasma sintered (66,7-x)Ti-xZn-22,2Si-11,1B alloys (at.-%, with x = 2 and ...6 at.-%). Ball milling at different times (20, 60, 180 and 300 min) was performed under argon atmosphere in a planetary ball mill from these elemental powder mixtures. Cylinder bodies with 10 mm diameter were consolidated by spark plasma sintering (1100 °C, 12 min, 20 MPa) under argon atmosphere. As-milled powders and sintered Ti-Zn-Si-B samples were evaluated by X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry, laser diffraction particle size analysis, and Vickers hardness tests. It was noted a similar behavior during ball milling of Ti-Zn-Si-B powder mixtures. Only the α-Ti and Si peaks were indexed in XRD patterns of Ti-Zn-Si-B powders milled for 300 min. Rietveld refining indicated that the amount of amorphous structures has increased during milling up to 300 min, which was more pronounced for the Ti-6Zn-22Si-11B powders. The particle sizes of the Ti-2Zn-22Si-11B and Ti-6Zn-22Si-11B powder mixtures increased during milling from 94 (20 min) to 156 (300 min) μm and from 101 (20 min) to 136 (300 min) μm, respectively. Coherently, the average specific surface area of powder particles was continuously reduced during milling. Despite the adopted parameters, the SPS process produced dense Ti-xZn-22Si-11B (x = 2 and 6 at.-%) alloys with 98% from their theoretical specific mass. Regardless of milling time, the Ti6Si2B formation was inhibited in microstructure of the spark plasma sintered Ti-6Zn-22Si-11B alloy previously milled for longer times. EDS analysis indicated that the Ti6Si2B phase dissolved close to 1.8 at.-% Zn. Beside the TiB and Ti5Si3, the Ti2Zn and Ti3Zn (not explored) phases were also found in microstructure of sintered Ti-Zn-Si-B alloys. The Ti-2Zn-22Si-11B alloy presented average Vickers hardness values higher than 1050 HV whereas the Ti-6Zn-22Si-11B alloy varied between 970 and 1036 HV, which could be associated with the Ti6Si2B formation.
•Spark plasma sintering produced dense Ti-Zn-Si-B samples.•Ti6Si2B has dissolved up to 1.8 at.-% Zn in alloy with 2 at.-% Zn.•Ti2Zn and Ti3Zn (not explored) were also formed in alloy with 6 at.-% Zn.•Ti-2Zn-22Si-11B alloy exihbited higher Vickers hardness than the alloy with 6 at.-% Zn.
Ti-6Al-4V and TiAl-based alloys are widely used for fabricating the implantable orthopedic devices and automotive components, respectively. Ti6Si2B-based alloys are attractive for use in orthopedic ...components because their higher hardness, superior biocompatibility and corrosion resistance in simulated body fluid than Ti and Ti-6Al-4V alloy. Limited information on Ti6Si2B stability in Co-dopped 67Ti-22Si-11B alloys are available in literature. This work presents the effect of cobalt doping and milling time on microstructure and Vickers microhardness of 65Ti-2Co-22Si-11B and 61Ti-6Co-22Si-11B (at-%) alloys produced by spark plasma sintering at 1100 oC for 12min using 20MPa. Samples were characterized by X ray diffraction, scanning electron microscopy, energy dispersive spectrometry, laser particle size analysis, and Vickers microhardness. Sintered alloys with 2 and 6at-%Co indicated the major presence of Ti6Si2B and Ti5Si3 dissolving up to 2.7 and 4.2 at-%Co, respectively, besides the minor precipitates of CoTi2 (4.4-16.7at-%Si) and CoTi (4.6-4.7at-%Si). Vickers microhardness of the sintered 65Ti-2Co-22Si-11B and 61Ti-6Co-22Si-11B alloys were in the range of 950-1050 and 1050-1150HV, respectively. Although the increase from 2 to 6at-%Co has reduced the Ti6Si2B stability, the Co-rich phases increased their hardness values up to 1150HV (11.3GPa), which are superior than those of commercial Ti alloys used for joint orthopedic components and automotive rotating parts.
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