Research

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17 pages, 5141 KiB

Open AccessArticle

Study of the Effect of the Floating Die Compaction on Mechanical Properties of Titanium Foams

by Sergio Sauceda, Sheila Lascano, Luis Béjar, Guilherme O. Neves, Ernesto Chicardi, Christopher Salvo and Claudio Aguilar

Metals 2020, 10(12), 1621; https://doi.org/10.3390/met10121621 - 02 Dec 2020

Cited by 3 | Viewed by 2578

Abstract

Titanium (Ti) and its alloys are used for biomedical applications because of their high resistance to corrosion, good strength-to-weight ratio, and high fatigue resistance. However, a problem that compromises the performance of the material is the mismatch between Young’s modulus of Ti and [...] Read more.

Titanium (Ti) and its alloys are used for biomedical applications because of their high resistance to corrosion, good strength-to-weight ratio, and high fatigue resistance. However, a problem that compromises the performance of the material is the mismatch between Young’s modulus of Ti and the bone, which brings about stress shielding. One strategy that has been investigated to reduce this difference is the manufacture of Ti-based foams, using powder metallurgy (PM) methods, such as the space-holder technique. However, in the uniaxial compaction, both non-uniform density distribution and mechanical properties remain because of the compaction method. This work studies the influence of compaction by adopting a floating-action die related to a single-action die (SAD), on the density of green and sintered Ti foams with porosities around 50 vol.% characterized by optical microscopy, ultrasound analysis, compression tests, and microhardness. The compaction process employing a floating-action die generates Ti foams with a higher density up to 10% with more control of the spacer particle added compared to the single-action die. Furthermore, compaction method has no relevant effect on microhardness and Young’s modulus, which allows getting better consolidated samples with elastic modules similar to those of human bone. Full article

(This article belongs to the Special Issue Powder Metallurgy of Titanium Alloys)

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7 pages, 2211 KiB

Open AccessCommunication

The Sticking Out Mechanism and Growth of TiB Whiskers from TiBw/Ti-6Al-4V Composites during Sintering

by Guorong Cui, Bo Yang, Jiabin Hou, Wenzhen Chen and Wencong Zhang

Metals 2020, 10(11), 1467; https://doi.org/10.3390/met10111467 - 04 Nov 2020

Cited by 5 | Viewed by 1443

Abstract

The process of TiB whiskers (TiBw) squeezed out and the growth of sticking out TiBw were investigated in TiBw/Ti-6Al-4V composites via adding 5 vol% TiB₂ powders. TiB₂ distributed along the surface of Ti-6Al-4V powders by low energy milling, resulted in the [...] Read more.

The process of TiB whiskers (TiBw) squeezed out and the growth of sticking out TiBw were investigated in TiBw/Ti-6Al-4V composites via adding 5 vol% TiB₂ powders. TiB₂ distributed along the surface of Ti-6Al-4V powders by low energy milling, resulted in the enrichment region of B and Ti elements. During sintering, TiBw nucleated and grew along the [010] direction with the diffusion of B and Ti atoms in the enrichment region. Due to larger thermal expansion ratio of TiBw, the TiBw were squeezed out from the Ti matrix, and the sticking out TiBw grew gradually with the diffusion of B and Ti atoms from the enrichment region. Because of the high interfacial strength between TiBw and Ti matrix, the matrix adhered to TiBw, and hindered the squeezing out of TiBw. Eventually, the cone TiBw stuck out the Ti matrix, and the other end of TiBw pinned in Ti matrix. Moreover, the diameter of TiBw near surface between TiB₂ and Ti matrix was larger than other areas, resulting from the high concentration of B and Ti atoms. The solubilized B atoms near TiBw were absorbed by TiBw, which was considered as the other B source of TiBw. Full article

(This article belongs to the Special Issue Powder Metallurgy of Titanium Alloys)

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15 pages, 6635 KiB

Open AccessArticle

Thermomechanical Processing of Cost-Affordable Powder Metallurgy Ti-5Fe Alloys from the Blended Elemental Approach: Microstructure, Tensile Deformation Behavior, and Failure

by Carlos Romero, Fei Yang, Shanghai Wei and Leandro Bolzoni

Metals 2020, 10(11), 1405; https://doi.org/10.3390/met10111405 - 22 Oct 2020

Cited by 7 | Viewed by 1784

Abstract

The development of cost-affordable Ti alloys is key for the application of Ti in other industries like the automobile sector. Therefore, a combination of powder metallurgy (PM) and low-cost compositions is an interesting approach. In this article, a cost-affordable PM Ti-5Fe alloy is [...] Read more.

The development of cost-affordable Ti alloys is key for the application of Ti in other industries like the automobile sector. Therefore, a combination of powder metallurgy (PM) and low-cost compositions is an interesting approach. In this article, a cost-affordable PM Ti-5Fe alloy is processed following the blended elemental route and extruded at high temperature to remove porosity. Different extrusion temperatures and heat treatments (i.e., solution treatment and aging, STA) are performed to obtain ultrafine microstructures, and their effect on the mechanical behavior is studied. For extrusions in the β phase, microstructures consist of coarse lamellar colonies, resulting in alloys with improved properties compared to the as-sintered alloy but still lacking toughness due to the failure happening just after necking onset. Extruding in the α + β phase results in a bimodal microstructure of fine elongated primary α and coarse lamellar colonies, and the alloy becomes tougher. STA with aging below the eutectoid temperature of 590 °C leads to a hard but brittle alloy, whereas STA with aging above it results in alloys with strength comparable to the as-extruded conditions and enhanced ductility. Full article

(This article belongs to the Special Issue Powder Metallurgy of Titanium Alloys)

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19 pages, 3175 KiB

Open AccessArticle

Beta Titanium Alloys Produced from Titanium Hydride: Effect of Alloying Elements on Titanium Hydride Decomposition

by Caterina Chirico, Sophia Alexandra Tsipas, Pablo Wilczynski and Elena Gordo

Metals 2020, 10(5), 682; https://doi.org/10.3390/met10050682 - 22 May 2020

Cited by 15 | Viewed by 3843

Abstract

The use of titanium hydride as a raw material has been an attractive alternative for the production of titanium components produced by powder metallurgy, due to increased densification of Ti compacts, greater control of contamination and cost reduction of the raw materials. However, [...] Read more.

The use of titanium hydride as a raw material has been an attractive alternative for the production of titanium components produced by powder metallurgy, due to increased densification of Ti compacts, greater control of contamination and cost reduction of the raw materials. However, a significant amount of hydrogen that often remains on the samples could generate degradation of the mechanical properties. Therefore, understanding decomposition mechanisms is essential to promote the components’ long life. Several studies on titanium hydride (TiH₂) decomposition have been developed; nevertheless, few studies focus on the effect of the alloying elements on the dehydrogenation process. In this work, the effects of the addition of different amounts of Fe (5 and 7 wt. %) and Nb (12, 25, and 40 wt. %) as alloying elements were evaluated in detail. Results suggest that α→β transformation of Ti occurs below 800 °C; β phase can be observed at lower temperature than the expected according to the phase diagram. It was found that β phase transformation could take place during the intermediate stage of dehydrogenation. A mechanism was proposed for the effect of allying elements on the dehydrogenation process. Full article

(This article belongs to the Special Issue Powder Metallurgy of Titanium Alloys)

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21 pages, 7433 KiB

Open AccessFeature PaperArticle

Oxidation and Corrosion Behavior of New Low-Cost Ti-7Fe-3Al and Ti-7Fe-5Cr Alloys from Titanium Hydride Powders

by Eduardo Reverte, Sophia A. Tsipas and Elena Gordo

Metals 2020, 10(2), 254; https://doi.org/10.3390/met10020254 - 14 Feb 2020

Cited by 9 | Viewed by 3214

Abstract

High production costs of Ti alloys usually hinders their use in industry sectors like the automotive and hence, low-cost titanium alloys could broaden titanium alloy usage. This work presents the study of three alloys— Ti-Fe, Ti-Fe-Al, and Ti-Fe-Cr—produced by powder metallurgy methods. The [...] Read more.

High production costs of Ti alloys usually hinders their use in industry sectors like the automotive and hence, low-cost titanium alloys could broaden titanium alloy usage. This work presents the study of three alloys— Ti-Fe, Ti-Fe-Al, and Ti-Fe-Cr—produced by powder metallurgy methods. The design of the compositions was aimed at reducing cost and enhance the oxidation and corrosion resistance while not decreasing the mechanical performance. The use of titanium hydride as raw material instead of Ti powder is highlighted as a key feature in the design and manufacturing procedure of the alloys. Introducing a dehydrogenation process during sintering favors the densification process while reducing the oxygen contamination and the production cost. There is a lack of studies focused on the implementation of affordable PM Ti alloys in high demanding environments. Therefore, a study of high temperature oxidation resistance and electrochemical behavior was performed. Full article

(This article belongs to the Special Issue Powder Metallurgy of Titanium Alloys)

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11 pages, 13240 KiB

Open AccessArticle

Microstructure and Mechanical Properties of Ti6Al4V Alloy Consolidated by Different Sintering Techniques

by Doan Dinh Phuong, Luong Van Duong, Nguyen Van Luan, Nguyen Ngoc Anh and Pham Van Trinh

Metals 2019, 9(10), 1033; https://doi.org/10.3390/met9101033 - 23 Sep 2019

Cited by 7 | Viewed by 3380

Abstract

In this paper, we investigated the effect of the different sintering techniques including vacuum sintering, capsule-free hot isostatic pressing (HIP), and capsule HIP on the microstructure and mechanical properties of Ti6Al4V alloy. The obtained results indicated that full density Ti6Al4V alloy could be [...] Read more.

In this paper, we investigated the effect of the different sintering techniques including vacuum sintering, capsule-free hot isostatic pressing (HIP), and capsule HIP on the microstructure and mechanical properties of Ti6Al4V alloy. The obtained results indicated that full density Ti6Al4V alloy could be obtained by using capsule HIP technique. The alloy sintered by capsule HIP had the highest hardness (~405 HV) and compressive yield strength (~1056 MPa). It is interesting that the geometry has a significant influence on the relative density and mechanical properties of the alloy sintered by the capsule-free HIP. The relative density, hardness, and compressive yield strength rise from center to periphery of the specimen. This is attributed to the heating and pressing in the capsule-free, which are external, leading to the densification processes starting from the outside to the inner parts of the pressed specimen. Using theoretical prediction with Gibson and Ashby power law found that the yield strength of the alloy sintered by capsule-HIP technique is much lower than that of the calculated value due to the formation of the coarse lamellar microstructure of α-Ti grains. Full article

(This article belongs to the Special Issue Powder Metallurgy of Titanium Alloys)

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18 pages, 6001 KiB

Open AccessArticle

Porous Titanium Surfaces to Control Bacteria Growth: Mechanical Properties and Sulfonated Polyetheretherketone Coatings as Antibiofouling Approaches

by Ana M. Beltrán, Ana Civantos, Cristina Dominguez-Trujillo, Rocío Moriche, José A. Rodríguez-Ortiz, Francisco García-Moreno, Thomas J. Webster, Paul H. Kamm, Andrea Mesa Restrepo and Yadir Torres

Metals 2019, 9(9), 995; https://doi.org/10.3390/met9090995 - 10 Sep 2019

Cited by 13 | Viewed by 2865

Abstract

Here, titanium porous substrates were fabricated by a space holder technique. The relationship between microstructural characteristics (pore equivalent diameter, mean free-path between pores, roughness and contact surface), mechanical properties (Young’s modulus, yield strength and dynamic micro-hardness) and bacterial behavior are discussed. The bacterial [...] Read more.

Here, titanium porous substrates were fabricated by a space holder technique. The relationship between microstructural characteristics (pore equivalent diameter, mean free-path between pores, roughness and contact surface), mechanical properties (Young’s modulus, yield strength and dynamic micro-hardness) and bacterial behavior are discussed. The bacterial strains evaluated are often found on dental implants: Methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa. The colony-forming units increased with the size of the spacer for both types of studied strains. An antibiofouling synthetic coating based on a sulfonated polyetheretherketone polymer revealed an effective chemical surface modification for inhibiting MRSA adhesion and growth. These findings collectively suggest that porous titanium implants designed with a pore size of 100–200 µm can be considered most suitable, assuring the best biomechanical and bifunctional anti-bacterial properties. Full article

(This article belongs to the Special Issue Powder Metallurgy of Titanium Alloys)

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12 pages, 4332 KiB

Open AccessArticle

Mechanical Properties and the Microstructure of β Ti-35Nb-10Ta-xFe Alloys Obtained by Powder Metallurgy for Biomedical Applications

by Angélica Amigó, Angel Vicente, Conrado R. M. Afonso and Vicente Amigó

Metals 2019, 9(1), 76; https://doi.org/10.3390/met9010076 - 12 Jan 2019

Cited by 14 | Viewed by 3287

Abstract

Titanium alloys with high refractory metals content are required to obtain advanced biomaterials with a low elastic modulus and good mechanical properties. This work studies the influence of Fe content on the microstructure and mechanical properties of powder metallurgy Ti35Nb10Ta(Fe) alloys, with Fe [...] Read more.

Titanium alloys with high refractory metals content are required to obtain advanced biomaterials with a low elastic modulus and good mechanical properties. This work studies the influence of Fe content on the microstructure and mechanical properties of powder metallurgy Ti35Nb10Ta(Fe) alloys, with Fe content additions of 1.5, 3.0 and 4.5 wt%. Samples are obtained by uniaxial compaction and sintering at 1250 °C and 1300 °C. Microstructural characterization is performed by scanning and transmission electron microscopy and mechanical characterization by bending, compression and a hardness test. The elastic modulus is measured by the ultrasounds technique. The results show a 10% increase in the maximum bending strength with an increase in the sintering temperature. The obtained microstructure is composed of β-Ti phase (bcc) and some regions where laths of the α-Ti (hcp) phase occur along the grain boundaries. Fe addition slightly improves the stability of the β-Ti phase and conversely decreases the maximum strength and final deformability due to increased porosity. The Ti35Nb10Ta alloy composition displays better properties, with an elastic modulus of 75 GPa, a bending strength of 853 MPa and compression strength of 1000 MPa. Full article

(This article belongs to the Special Issue Powder Metallurgy of Titanium Alloys)

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10 pages, 4496 KiB

Open AccessArticle

High-Temperature Compressive Properties of TiB-Reinforced Ti Alloy via In Situ Synthesis

by Jing Zeng, Liping Liu, Jiazhi Yuan and Hua Chen

Metals 2018, 8(5), 303; https://doi.org/10.3390/met8050303 - 27 Apr 2018

Cited by 1 | Viewed by 2829

Abstract

In this investigation, in situ synthesis of TiB-reinforced Ti-based alloy was carried out by powder metallurgy. The Ti (TiH₂)—Al and B powders were ball milled for 40 h to obtain a mixed powder with a nominal composition of Ti-7Al-0.2B (wt. %) [...] Read more.

In this investigation, in situ synthesis of TiB-reinforced Ti-based alloy was carried out by powder metallurgy. The Ti (TiH₂)—Al and B powders were ball milled for 40 h to obtain a mixed powder with a nominal composition of Ti-7Al-0.2B (wt. %) and TiH₂-7Al-0.2B (wt. %). After milling the mixed powder by using a vacuum hot pressing sintering furnace (1200 °C sintering temperature, 30 MPa pressure, 1 h holding pressure), TiB-reinforced Ti-based alloy was prepared in situ. The compression tests were carried out on a WDW-200 universal testing machine at 550 °C, 600 °C, and 650 °C, and at the strain rates of 1 × 10⁻⁴ s⁻¹, 3 × 10⁻⁴ s⁻¹, and 5 × 10⁻⁴ s⁻¹ to investigate the alloy compression and rheological behavior of the prepared alloy. It was observed that Ti-7Al-0.2B and TiH₂-7Al-0.2B alloy formed a TiB phase and α-Ti duplex structure after low-energy ball milling and hot pressed sintering. This is because the in situ synthesis of TiB fiber reinforced phase hinders grain boundary migration and grain growth. Therefore, the TiB phase in Ti-7Al-0.2B alloy is fine, evenly distributed and effective in suppressing grain growth. Alloy materials are heat sensitive and strain-rate sensitive alloys, and the peaks of high-temperature compressive stress decrease with the decrease of the strain rate and the increase of the temperature. At the same temperature and rate conditions, the highest peak flow stress of TiH₂-7Al-0.2B is slightly higher than that of Ti-7Al-0.2B. In the ball milling and sintering process of TiH₂-7Al-0.2B alloy, the decomposition of H from TiH₂ cleanses the surface of Ti particles. This leads to the reduction of the possibility of contamination, and also has a good effect in improving the compression performance. Full article

(This article belongs to the Special Issue Powder Metallurgy of Titanium Alloys)

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Review

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18 pages, 11471 KiB

Open AccessReview

Near Net Shape Manufacture of Titanium Alloy Components from Powder and Wire: A Review of State-of-the-Art Process Routes

by Thomas Childerhouse and Martin Jackson

Metals 2019, 9(6), 689; https://doi.org/10.3390/met9060689 - 15 Jun 2019

Cited by 35 | Viewed by 12770

Abstract

Near net shape (NNS) manufacturing offers an alternative to conventional processes for the manufacture of titanium alloy components. Compared to the conventional routes, which typically require extensive material removal of forged billets, NNS methods offer more efficient material usage and can significantly reduce [...] Read more.

Near net shape (NNS) manufacturing offers an alternative to conventional processes for the manufacture of titanium alloy components. Compared to the conventional routes, which typically require extensive material removal of forged billets, NNS methods offer more efficient material usage and can significantly reduce machining requirements. Furthermore, NNS manufacturing processes offer benefits such as greater flexibility and reduced costs compared to conventional methods. Processes such as metal additive manufacturing (AM) have started to be adopted in niche applications, most notably for the manufacture of medical implants, where many conventionally forged components have been replaced by those manufactured by AM processes. However, for more widespread adoption of these emerging processes, an improvement in the confidence in the techniques by manufacturers is necessary. This requires addressing challenges such as the limited mechanical properties of parts in their as-built condition compared to wrought products and the post-process machining requirements of components manufactured by these routes. In this review, processes which use a powder or wire feedstock are evaluated to assess their capabilities for the manufacture of titanium alloy components. These processes include powder bed fusion and direct energy deposition metal additive processes as well as hybrid routes, which combine powder metallurgy with thermomechanical post-processing. Full article

(This article belongs to the Special Issue Powder Metallurgy of Titanium Alloys)

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