211 research outputs found
Recent development in beta titanium alloys for biomedical applications
© 2020 by the authors. Licensee MDPI, Basel, Switzerland. β-type titanium (Ti) alloys have attracted a lot of attention as novel biomedical materials in the past decades due to their low elastic moduli and good biocompatibility. This article provides a broad and extensive review of β-type Ti alloys in terms of alloy design, preparation methods, mechanical properties, corrosion behavior, and biocompatibility. After briefly introducing the development of Ti and Ti alloys for biomedical applications, this article reviews the design of β-type Ti alloys from the perspective of the molybdenum equivalency (Moeq) method and DV-Xα molecular orbital method. Based on these methods, a considerable number of β-type Ti alloys are developed. Although β-type Ti alloys have lower elastic moduli compared with other types of Ti alloys, they still possess higher elastic moduli than human bones. Therefore, porous β-type Ti alloys with declined elastic modulus have been developed by some preparation methods, such as powder metallurgy, additive manufacture and so on. As reviewed, β-type Ti alloys have comparable or even better mechanical properties, corrosion behavior, and biocompatibility compared with other types of Ti alloys. Hence, β-type Ti alloys are the more suitable materials used as implant materials. However, there are still some problems with β-type Ti alloys, such as biological inertness. As such, summarizing the findings from the current literature, suggestions forβ-type Ti alloys with bioactive coatings are proposed for the future development
The structure and properties of additively manufactured metastable-β Ti-15Mo
A bidirectional powder deposition strategy was employed to additively manufacture Ti-15Mo wt% using laser metal deposition. Phase identification, elemental analysis and microstructural characterisation were conducted in the As-Built condition and also after uniaxial tensile testing using X-ray diffraction and scanning electron microscopy along the different processing directions. In addition, electron backscattering diffraction and transmission electron microscopy were used to analyse deformation mechanisms. It was found that three distinct zones, namely the fusion, remelted and heat affected zones, evolved in all 25 deposited layers which predominantly comprised coarse columnar grains. These columnar grains were coarser up the build height due to increased distance from the substrate and slower cooling rates determined. Mo segregation was pronounced in the as-built microstructure. The fusion zone was the most solute enriched zone, followed by the remelted zone. The heat affected zone of each deposited layer featured inter-dendritic lamellas of molybdenum rich and lean inter-layers and this zone was the least solute-enriched. Deformation accommodation in β matrix was by a combination of slip, {332}〈113〉 and {112}〈111〉 twinning, α martensite and ωD formation contrarily to the expected twinning.
The as-built alloy was subsequently subject to post-fabrication heat treatment. Microstructural characterisation was conducted in the heat-treated state and also after uniaxial tensile deformation. X-ray diffraction, energy dispersive spectroscopy and scanning electron microscopy were employed in the heat-treated state. Electron backscatter diffraction was used in investigating the deformed microstructure. Columnar β grain refinement was achieved by fragmentation from a combined contribution from precipitated phases and deformation induced products. The three distinct microstructural zones, namely the fusion, remelted and heat affected zones, observed in each deposited layer of the as-built microstructure were retained after sub-β-solvus heat treatment but completely erased in the super-β-solvus microstructure. Accommodation of plastic deformation in β matrix was by a combination of slip and primary α martensite which formed preferentially at grain boundaries. Elastic modulus decreased from 86.85±0.45 GPa in the as-built alloy to 72.8±0.65 GPa after heat treatment. Ultimate tensile strength of 1168± 1.12 MPa from the heat-treated sample represents only a marginal increase from that of the as-built sample of 1099± 2.3 MPa. This was accompanied by a small decrease in total elongation.
The as-built alloy was also subject to post-fabrication uniaxial thermomechanical processing at strain rates of 0.00055s-1, 0.0011s-1, 1s-1, and 4s-1 to strains of 20% and 40%. Experiments were conducted at room and elevated temperatures. Phase identification, elemental and microstructural characterisation were conducted using x-ray diffraction, energy dispersive spectroscopy and scanning electron microscopy. The three distinct zones, namely the fusion, remelted and heat affected zones, identified in each deposited layer of the as-built microstructure were retained after thermomechanical processing. After processing, electron backscatter diffraction was used to analyse deformation mechanisms. Deformation accommodation in β matrix was predominantly by a combination of slip and α martensite which formed as a primary product in parent β and at grain boundaries. However, the operation of {332}〈113〉 and {112}〈111〉 β-twinning was also determined, howbeit with a very small surface fraction. This implies a small surface fraction of secondary α martensite forming within β-twins in the deformed microstructure. Compressive mechanical properties showed a strong dependence on strain rate as higher flow stress and compressive strength were obtained at higher strain rates
Development of new high performance Titanium alloys with Fe-addition for dental implants
[EN] Ti and its alloys are mostly used biomaterials due to its unique properties like (high
corrosion resistance, low elastic modulus, high mechanical strength/ density and
good biocompatibility). Ti β alloys based on the Ti-Mo alloy system shows unique
properties to employ as biomaterials. Tiβ alloys have lower Young Modulus,
shielding stress and lower bone reabsorption. This research aims to develop a new
biomaterial for a dental implant.
This research evaluates the addition of Zr and a small amount of Fe on the β-phase
stability and the mechanical properties of Ti-Mo alloy to be employed for the
medical applications. These alloys had been produced using two powder metallurgy
(PM) techniques; first technique is elemental blending (EB) which had been selected
because it enhanced the surface contact between the alloying element and Titanium
(Ti) with a cost-effective route. The behavior of different Ti alloys composition was
evaluated using this technique. Samples were uniaxial pressed at 600 MPa and
sintered at 1250ºC. Second technique evaluated in this study was Mechanical
alloying (MA). This technique has higher mixing energy than elemental blend which
improves mechanical contact between different particles, and it helps diffusion
during the sintering process. Samples were pressed at 600 MPa initially, and after
evaluating mechanical properties, compaction pressure is changed to 900 MPa for a
high green density of powders.
Different mechanical tests and microstructural studies were performed for elemental
blend (EB) samples and for mechanical alloying samples to ensure the properties
suitable for biomedical applications. Different tests for MA are Fluidity test (suitable
to know about the flow of the powder after milling cycle) and Granulometric
Analysis (test is suitable for powder distribution analysis). Other tests are common
like Archimedes test which is suitable for calculating the porosity of the sintered
samples, Three-point bending test is suitable for knowing Bending strength of the
sintered samples and to know energy conserved by the breaking samples, Ultrasonic test performed for knowing elastic modulus of the alloys, Hardness test performed
for calculating the Vicker´s hardness of the alloy, SEM analysis performed to know
about microstructure and EDX analysis(by which proper mixing of the alloying
element with the central element would be known). EBSD (Electron Beam Scattered
Diffraction) is also performed for more analysis about microstructure, grain size,
mixing of different elements in alloys. EBSD is an excellent tool for microanalysis
of the material.
From the results section, Green density of the alloy, fluidity of the milled powder,
Granulometry of the powder, sintered density of the alloy (From Archimedes test),
bending strength and bending modulus of the alloy, Elastic modulus by Ultrasonic
test, Microstructure of the alloy(By SEM and EBSD Analysis of the sintered part.)
are determined. Green density for elemental blend alloys is in the range of (77.42-
78.11%) and for Mechanical alloying samples were (74.94-78.58%). Sintered
density obtained by Archimedes' test for the elemental blend is in the range of (96.88-
98.74%). Bending strength obtained from three-point bending test is in range of
(666-2161 MPa), and mechanical alloying is in range of (371-1597 MPa). From the
high test, Determined Elastic modulus of the alloy is in range of (95.5-103 GPa) and
for Mechanical Alloying elastic modulus was in the range of (66-82 GPa), which
would be more suitable for biomedical applications. (From the SEM and EBSD
analysis Mechanical alloying are more homogeneous mixing in comparison to
Elemental Blend.
Green density (just after compaction) for the elemental blend is more than
mechanical alloying so that Sintered Density for Elemental Blend is more than
Mechanical Alloying. Due to higher sintered density, porosity is more in case of the
elemental blend. Also, due to higher porosity, bending strength is low in case of
mechanical alloying with same sintering parameters as Elemental blend alloys.
Micro-Hardness value is more in case of elemental blend in comparison to
Mechanical Alloying. Elastic modulus is more in case of elemental blend in
comparison to mechanical alloying; lower elastic modulus is more suitable for
biomedical applications. Grains are more regular and smaller in case of Mechanical
alloying which is due to a more homogeneous distribution of the elements in
comparison to elemental blend.
Powder processing technique is changed from Elemental Blend to Mechanical
Alloying due to the improvement of homogeneity of green powders. Mechanical
Alloying produced more homogeneous mixture due to high-speed milling with
higher Ball to powder ratio (which generates higher energy within the jars and breaks
the powders into smaller particles). Different combination of milling speed and
milling time performed for our results and the effects of a combination of different
parameters observed.[ES] El titanio y sus aleaciones son los biomateriales principalmente usados debido a sus
propiedades únicas como alta resistencia a la corrosión, bajo módulo de elasticidad,
alta resistencia mecánica/densidad y buena biocompatibilidad. Las aleaciones Tiβ
basadas en el sistema de aleación Ti-Mo muestran propiedades únicas para
emplearse como biomateriales. Las aleaciones de Tiβ tienen un módulo de Young
más bajo, menor apantallamiento de tensiones y menor reabsorción ósea. Esta
investigación tiene como objetivo desarrollar un nuevo material biológico para un
implante dental.
Esta investigación evalúa la adición de Zr y una pequeña cantidad de Fe sobre la
estabilidad de fase β y las propiedades mecánicas de la aleación de Ti-Mo que se
utilizará para las aplicaciones médicas. Estas aleaciones se han producido utilizando
dos técnicas de pulvimetalurgia (PM); La primera técnica es la combinación de
polvos elementales (EB) que se ha seleccionado porque mejora el contacto
superficial entre el elemento de aleación y el titanio (Ti) con una ruta rentable. El
comportamiento de diferentes composiciones de aleaciones de Ti se evaluó
utilizando esta técnica. Las muestras se prensaron uniaxialmente a 600 MPa y se
sinterizaron a 1250ºC. La segunda técnica evaluada en este estudio fue la aleación
mecánica (MA). Esta técnica tiene una mayor energía de mezcla que la mezcla
elemental, lo que mejora el contacto mecánico entre las diferentes partículas y ayuda
a la difusión durante el proceso de sinterización. Las muestras se prensaron,
igualmente, a 600 MPa inicialmente, y después de evaluar las propiedades
mecánicas, la presión de compactación se aumentó a 900 MPa para una mayor
densidad en verde de los polvos.
Se realizaron diferentes pruebas mecánicas y estudios microestructurales para las
muestras de mezcla elemental (EB) y las muestras de aleación mecánica (MA) para
garantizar las propiedades adecuadas para aplicaciones biomédicas. Las diferentes pruebas para MA han sido la fluidez, adecuada para conocer el flujo del polvo
después del ciclo de molienda, y el análisis granulométrico, adecuado para el análisis
de la distribución del tamaño de los polvos. Otras pruebas comunes como la
determinación de la densidad por el método de Arquímedes, adecuada para calcular
la porosidad de las muestras sinterizadas, el ensayo de flexión a tres puntos para
conocer las propiedades mecánicas de las muestras sinterizadas y conocer la energía
conservada por las muestras a rotura, y la dureza Vickers de las aleaciones. Mediante
ultrasonidos se ha determinado el módulo elástico de las aleaciones. El análisis
microestructural se ha realizado mediante microscopía electrónica de barrido y
análisis por energías dispersivas de rayos X mediante los que se ha determinado la
homogeneidad química de las aleaciones. La difracción de electrones
retrodispersados (EBSD) ha permitido obtener la orientación cristalina de cada grano
y su tamaño, pues resulta una excelente herramienta para el microanálisis del
material.
La densidad en verde para aleaciones de mezcla elemental está en el rango del 77.42-
78.11% y para las muestras de aleación mecánica se han obtenido densidades
relativas del 74.94-78.58%. La densidad de los sinterizados, obtenida por el método
de Arquímedes, está en el rango del 96.88-98.74%, para la mezcla elemental de
polvos. La resistencia a la flexión obtenida a partir de la prueba de flexión a tres
puntos está en un amplio rango de 666 a 2161 GPa, mientras que para los polvos de
aleación mecánica se encuentra en el rango de los 371 a 1597 GPa. El módulo
elástico determinado en las aleaciones obtenidas con polvos de mezcla elemental
está en el rango de los 95.5 a los 103 GPa, mientras que, en las obtenidas con los
polvos mezclados mecánicamente, su módulo elástico oscila entre los 66 y los 82
GPa, que sería más adecuado para un menor apantallamiento de tensiones. La
microestructura de las muestras procesadas con polvos elementales con polvos
mezclados mecánicamente, presentan diferencias sustanciales con un afinamiento
del tamaño de grano con los polvos mezclados mecánicamente, aunque aparecen
claramente diferenciadas dos fases distintas y una mayor proporción de fase .
Debido a la menor densidad de las muestras procesadas con los polvos mezclados
mecánicamente, estas presentan una menor resistencia mecánica y a su vez una
menor plasticidad. Por ello se opta por utilizar técnicas de sinterización de alta
densificación como el Spark Plasma Sinterirng (SPS) a pesar de lo cual no obtenemos mejora en el comportamiento mecánico de las mismas. Sin embargo, en
los ensayos de corrosión y liberación de iones si se ha encontrado una sustancial
mejor en las muestras obtenidas por SPS.[CA] El titani i els seus aliatges són utilitzats, principalment, com a biomaterials per les
seves propietats úniques com alta resistència a la corrosió, baix mòdul d'elasticitat,
alta resistència mecànica específica i bona biocompatibilitat. Els aliatges β Ti
basades en el sistema d'aliatge Ti-Mo mostren propietats úniques per a emprar-se
com biomaterials. Els aliatges de β Ti tenen un mòdul de Young més baix, menor
apantallament de tensions i menor reabsorció òssia. Aquesta investigació té com a
objectiu desenvolupar un nou material biocompatible per a la seva aplicació com a
implants dentals.
Aquesta investigació avalua l'addició de Zr i petites quantitats de Fe sobre l'estabilitat
de la fase β i les propietats mecàniques dels aliatges Ti-Mo que s'utilitzaran per a
aplicacions biomèdiques. Aquests aliatges s'han produït utilitzant dues tècniques
pulvimetalúrgiques (PM); La primera tècnica és la mescla elemental de pols (EB)
que s'ha seleccionat perquè millora el contacte superficial entre l'element d'aliatge i
el titani (Ti) amb una ruta rendible. El comportament de diferents composicions
d'aliatges de Ti s'ha avaluat utilitzant aquesta tècnica. Les mostres es van premsar
uniaxialment a 600 MPa i es sinteritzaren a 1250ºC. La segona tècnica avaluada en
aquest estudi va ser l'aliatge mecànica (MA). Aquesta tècnica té una major energia
de mescla que la mescla elemental, el que millora el contacte mecànic entre les
diferents partícules i ajuda a la difusió durant el procés de sinterització. Les mostres
es van premsar a 600 MPa inicialment, i després d'avaluar les propietats mecàniques,
la pressió de compactació es va augmentar a 900 MPa per a una major densitat en
verd de les pols.
Es van realitzar diferents proves mecàniques i estudis microestructurals per a mostres
de mescla elemental (EB) i per a mostres d'aliatge mecànica per garantir les
propietats adequades per a aplicacions biomèdiques. Les diferents proves per MA
són la prova de fluïdesa (adequada per conèixer el flux de la pols després del cicle
d'aliatge mecànica) i l'anàlisi granulomètric (la prova és adequada per a l'anàlisi de
distribució de la mida de les pols). S'han realitzat altres proves comunes com la prova
d'Arquímedes, adequada per a calcular la porositat de les mostres sinteritzades. La prova de flexió de tres punts és adequada per conèixer la resistència a la flexió de les
mostres sinteritzades i conèixer l'energia conservada per les mostres durant el seu
trencament. Mitjançant ultrasons s'ha determinat el mòdul elàstic dels aliatges i la
duresa s'ha realitzat per calcular la duresa Vickers de l'aliatge. S'ha realitzat l'anàlisi
per SEM per conèixer la microestructura i l'anàlisi per EDX (mitjançant el qual es
coneixeria la mescla adequada de l'element d'aliatge amb l'element central). EBSD
(difracció d'electrons retro dispersats) també es realitza per a un més complet anàlisi
sobre la microestructura, orientacions cristal·lines, mida de gra, mescla de diferents
elements en els aliatges. EBSD és una excel·lent eina per al microanàlisi del material.
De la secció de resultats es determinen la densitat en verd de l'aliatge, fluïdesa de la
pols mòlta, granulometria de la pols, densitat de l'aliatge sinteritzada (prova
d'Arquímedes), resistència a la flexió i mòdul a flexió de l'aliatge, mòdul elàstic per
ultrasons, microestructura de l'aliatge (per SEM i EBSD). La densitat en verd per als
aliatges de mescla elemental està en el rang dels 77.42-78.11%, mentre que per a les
mostres d'aliatge mecànica van ser d'un 74.94-78.58%. La densitat dels sinteritzats,
obtinguda pel mètode d'Arquímedes, està en el rang dels 96.88-98.74%, per la
mescla elemental de pols. La resistència a la flexió obtinguda a partir de la prova de
flexió de tres punts es troba en el rang dels 666-2161 MPa, mentre que per a les
mostres de aliat mecànic el seu rang és molt ampli, des dels 371 als 1597 MPa. A
partir de l'assaig d'ultrasons, el mòdul elàstic determinat per als aliatges de mescla
elemental està en el rang de 95.5 a 103 GPa i per a les sinteritzades amb pols aliats
mecànicament, es troba en el rang dels 66-82 GPa, que seria més adequat per a
aplicacions biomèdiques. A partir de les anàlisis per SEM i EBSD, es confirma que
l'aliatge mecànica és una mescla més homogènia en comparació amb la mescla
elemental dels pols.
La densitat en verd (just després de la compactació) per a la mescla elemental és més
gran que en l'aliatge mecànica, de manera que la densitat sinteritzada per a la mescla
elemental és major igualment que en l'aliatge mecànica. A causa d'una major densitat
dels sinteritzats, la porositat és menor en el cas de la mescla elemental. A més, a
causa d'una major porositat, la resistència a la flexió és baixa en cas d'aliatge
mecànica amb els mateixos paràmetres de sinterització que els aliatges de mescla
elemental. El valor de microduresa és major en el cas de la mescla elemental en comparació amb l'aliatge mecànica. El mòdul elàstic també resulta més gran en el
cas d'una mescla elemental comparat amb l'aliatge mecànica, que en aquest cas
resultaria més adequat per a aplicacions biomèdiques. Els grans són més regulars i
més petits en el cas de l'aliatge mecànica, a causa d'una distribució més homogènia
dels elements en comparació amb la mescla elemental i als efectes de
recristal·lització durant la sinterització.
L'aliatge mecànica va produir una mescla més homogènia dels elements d'aliatge, a
causa de la mòlta a alta velocitat amb una relació boles/pols més alta que genera una
major energia dins de les gerres i obté partícules de pols més petites. S'ha realitzat
una combinació de diferents velocitats i temps de mòlta, optimitzant aquests
paràmetres per a les nostres aliatges.Mohan, P. (2020). Development of new high performance Titanium alloys with Fe-addition for dental implants [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/147859TESI
Revised semiempirical approach to predict the occurrence of twinning in titanium alloys
A revised semiempirical approach, considering the average values of the valence electron to atom ratio (e/a̅) and a difference in atomic radii of alloying element/s and the base element (Δr¯), is proposed to predict the twin formation in titanium alloys. The revised e/ā versus Δr¯ diagram is plotted, considering the reported results of 90 titanium alloys fabricated using various processing methods. A new twin/slip boundary has been plotted and recommended based on the revised e/ā versus Δr¯ diagram. The conventional maximum limit reported for the twinning in titanium alloys is e/ā = 4.20; however, it has been found that twinning in titanium alloys is possible up to the e/ā of 4.30
On the role of composition and processing parameters on the microstructure evolution of Ti-xMo alloys
Abstract
Laser Engineered Net Shaping (LENS™) was used to produce a compositionally graded Ti-xMo (0 ≤ x ≤ 12 wt %) specimen and nine Ti-15Mo (fixed composition) specimens at different energy densities to understand the composition–processing–microstructure relationships operating using additive manufacturing. The gradient was used to evaluate the effect of composition on the prior-beta grain size. The specimens deposited using different energy densities were used to assess the processing parameters influence the microstructure evolutions. The gradient specimen did not show beta grain size reduction with the Mo content. The analysis from the perspective of the two grain refinement mechanisms based on a model known as the Easton & St. John, which was originally developed for aluminum and magnesium alloys shows the lower bound in prior-beta grain refinement with the Ti–Mo system. The low growth restriction factor for the Ti-Mo system of Q = 6,5C0 explains the unsuccessful refinement from the solute-based mechanism. The energy density and the grain size are proportional according to the results of the nine fixed composition specimens at different energy densities. More energy absorption from the material represents bigger molten pools, which in turn relates to lower cooling rates.https://deepblue.lib.umich.edu/bitstream/2027.42/147465/1/13065_2019_Article_529.pd
Structure Characterization of Biomedical Ti-Mo-Sn Alloy Prepared by Mechanical Alloying Method
The study presents the results of the influence of high energy milling on the structure of the new Ti–15Mo–
5Sn [wt%] alloy for biomedical applications. During testing the powders were milled for the following milling times:
5, 15, 30, and 45 h. The milled powders were characterized by X-ray diffraction, scanning and transmission electron
microscopy methods. Observation of the powder morphology after various stages of milling leads to the conclusion
that with the increase of the milling time the size of the powder particles as well as the degree of aggregation
change. However, a clear tendency of particles reduction at every stage of the mechanical alloying process is clearly
observed. The X-ray diffraction results confirmed the presence of the and phases, and molybdenum. It has
been found that the reflections from the Sn phase disappeared after five hours of milling, suggesting that the Sn and
Ti alloying took place, leading to the creation of a titanium-based solid solution. After 30 and 45 h of mechanical
alloying the formation of the -Ti phase, the final share of which is 46(4) wt%, was observed. Furthermore, it
was found that a diffraction line broadening with the increase of the milling time results from reduction of the
crystallite size and an increase in the lattice distortion. The maximum level of the reduction of the crystallite size
was obtained after 45 h of milling. The maximum degree of the unit cells reduction for all phases present in the
powder that was being milled was also observed for this milling time
Corrosion Behaviour of Titanium β Type Ti-12Cr in 3% NaCl Solution
Titanium alloy, especially titanium type Ti-12Cr for biomedical application has been a concern of many researchers recently. This titanium has excellent biocompatibility and controllable mechanical properties. Generally, titanium β type contains many alloying elements that lead to a high price. Therefore, it is interesting to develop β type with only one cheap alloying element such as Ti-12Cr that is designed as a low-cost implant material. Initially, Ti-12Cr has been developed, in particular for spinal fixation. Nowadays, the research of Ti-12Cr emphasizes only on mechanical properties. The corrosion behavior of this alloy has not been understood well yet. Therefore, corrosion characteristics of this alloy in any circumstances are necessary to investigate. This paper reports the corrosion behavior of Ti-12Cr in a salted environment using the weight loss method. Ti-12Cr samples were immersed in a 3% NaCl solution for 2, 4, and 6 weeks. Samples consist of Ti-12Cr (as-received), Ti-12Cr (ST) and Ti-12Cr (AT 30 ks). Weight of samples was measured before and after the immersing process using the digital balance. Microstructure and composition of the sample surfaces were examined by using SEM and EDX, respectively. The lowest corrosion rate after exposure for 6 weeks while the highest one is Ti-12Cr (as-received) is Ti-12Cr (AT 30 ks) that is 0,003 mmpy. The microstructure all of the samples shows black spots in the surfaces indicating corrosion has been started to occur on the samples. It was found that the corrosion is due to destruction of the chrome-oxide layer in some weak point as a result of a chemical reaction between the metal (Cr) with Cl- ions. Some oxides are formed on the surface of titanium, as indicated by a significant increment of oxygen content is the corrosive sample surface. This study indicates the corrosion resistance of Ti-12Cr (AT 30 ks) is much better than other materials in this research.
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