CP-Ti Grade Research Articles

Friction and heat partition coefficients in incremental sheet forming process

To understand the thermo-mechanical behaviour in incremental sheet forming (ISF), it is important to precisely determine the interfacial and thermal-relevant parameters including coefficient of friction (COF) and heat partition coefficient (HPC), and to characterise the effect of thermo-mechanically induced heat generation under ISF processing conditions. In the present study, a new tool path-defined straight groove test combined with mechanical and thermal detection is proposed to determine the COF and HPC of Aluminium alloy (AA1050) and commercially pure titanium Grade 1 (CP Ti Grade 1) sheets. The experimental and numerical results show that the determined COF and HPC values are sufficiently accurate. The interaction between friction force and thermal response is observed by this testing method. A novel theoretical thermal model is developed to correlate the relationship between friction-induced heat generation and the thermal effect. The results indicate that the new theoretical model can capture the temperature distribution and variation under different processing conditions, and the results show a good agreement with the finite element (FE) simulation. The presented testing method and theoretical model provide an insight into the determination of the thermal-relevant parameters (COF and HPC), and the quantification of the effect of friction-induced heat generation on the thermal response of the materials.

Numerical and experimental validation of CP-Ti (Grade 2) under cryogenic condition

A combined analytical and experimental study was carried out to investigate the effect of cryogenic cooling on temperature during turning of pure titanium grade-2. Cryogenic machining investigations were carried out by applying liquid nitrogen (LN2) to the cutting zone. The temperature distribution at the machined surface was predicted using a 3D finite element model. An average deviation of 7.42% was noted for the cutting temperature result, and there was good agreement between the simulated and experimental results. The experimental results reveal that LN2 machining improves cooling and lubrication by lowering the cutting zone temperature. Acceptable tool wear, surface roughness, and favourable chip formation are observed in LN2 machining at higher cutting speeds.

A roadmap for tailoring the microstructure and mechanical properties of additively manufactured commercially-pure titanium

In recent years there has been a growing interest in using additive manufacturing to produce near net-shape parts from titanium alloys. Most of these studies have focused on the fabrication of various high-strength alloys such as Ti5553 and Ti–6Al–4V, but there is also a desire to produce parts out of lower-strength and higher elasticity alloys such as commercially pure titanium (CP–Ti). In this work, we have shown the effects on various properties of CP-Ti Grade 2 produced via the Laser Powder Bed Fusion (L-PBF) manufacturing process and subsequent heat treatments. Samples with 99.98 % density were produced. Microstructure and phase evolution was characterized by X-ray and electron backscatter diffraction and polarized light microscopy. Oxygen was found to be incorporated during manufacture and processing by Inert Gas Fusion (IGF). Heat-treatment of the samples resulted in recrystallization of the acicular microstructure. By testing the mechanical properties throughout the recrystallization temperatures, it was observed that the grain recrystallization lead to a reduction in mechanical strength without a significant improvement in ductility, therefore making a low temperature heat-treatment that retains the AM microstructure an interesting alternative to strengthen CP-Ti.

Combined severe plastic deformation processing of commercial purity titanium enables superior fatigue resistance for next generation implants

Commercial purity titanium (cp-Ti) is considered for replacing Ti64 as an implant material in various applications, due to the potential toxicity associated with the release of Al and V ions. However, the mechanical properties of cp-Ti, particularly fatigue resistance, are inadequate for this purpose. In this study, cp-Ti grade 4 rods were processed using a combination of equal channel angular pressing and rotary swaging (ECAP/RS). Tensile and fatigue tests were conducted, along with detailed microscopy and evaluation of corrosion resistance and biocompatibility. An average yield strength of 1383 MPa was obtained while maintaining moderate ductility of 10 %. This represents the highest strength ever recorded for cp-Ti, even exceeding that of Ti64. Additionally, fatigue endurance limit increased by 43 % up to 600 MPa, almost obtaining that of Ti64. Strengthening mechanisms were attributed to the ultrafine-grained (UFG) microstructure generated by ECAP/RS, along with strong crystallographic texture and formation of sub-grain structure. Furthermore, the corrosion resistance and biocompatibility of cp-Ti were largely unaffected, potentially easing regulatory transition in future medical devices. Thus, these results demonstrate high potential of combined ECAP/RS processing to manufacture UFG cp-Ti grade 4 materials that prospectively allow for the substitution of questionable alloys and downsizing of medical implants.

Residual stress, fatigue behavior, and mechanical properties of equal-channel angular pressed commercial pure titanium

Residual stresses, fatigue behavior, and mechanical properties of equal channel angular pressing (ECAP) commercial pure titanium (CP–Ti) are investigated in this study. Residual stresses can significantly affect the performance and reliability of CP-Ti components under cyclic loading conditions. The study focuses on understanding the relationship between ECAP processing, residual stresses, and fatigue behavior in CP-Ti. The ECAP process was employed to produce CP-Ti grade 2 samples, and their fatigue behavior was characterized. The results revealed a significant increment in residual stresses, fatigue strength, microhardness, and tensile strength by ECAP processing on the CP-Ti. The measured fatigue limit of the processed CP-Ti was found to be higher than that of coarse-grained CP-Ti and approaches the fatigue limit of the Ti–6Al–4V alloy. Residual stresses resulting from non-conventional machining processes and surface treatments are known to affect the fatigue life of titanium alloys. Compressive residual stresses have been shown to inhibit the growth rate of fatigue cracks and improve fatigue life. Understanding the effect of residual stresses on the fatigue behavior and mechanical properties of ECAP-processed CP-Ti is crucial to optimizing the design and ensuring the long-term durability of CP-Ti components in engineering applications.

Effect of Friction Stir Welding on Short-Term Creep Response of Pure Titanium

Friction Stir Welding (FSW) is a recent joining technique that has received considerable attention. FSW causes significant variations in the material microstructure commonly associated with changes in the mechanical properties. The present study deals with the creep response of pure titanium (CP-Ti grade 2) after FSW. Dog-bone creep samples, obtained by machining, which show the longitudinal axis of each sample being perpendicular to the welding direction, were tested in constant load machines at 550 and 600 °C. The creep response of the FSW samples was analyzed and compared with that of the unwelded material. The shape of the creep curves was conventional, although the FSW samples went to rupture for strains lower than the base metal. The minimum creep rates for FSW samples were, in general, lower than for the unwelded metal tested in equivalent conditions. In addition, when the applied stress was high, deformation concentrated in the parent metal. The creep strain became more and more homogeneous along the gauge length as testing stress decreased. A constitutive model, recently developed for describing the creep response of the base metal, was then used to rationalize the observed reduction in the minimum strain rate in FSW samples.

Usability of the ECAP-Conform process for the production of dental implants material

This study addresses the applicability of the ECAP-Conform process for the production of strengthened titanium to produce dental implants. For this purpose, the commercially pure titanium (CP–Ti) grade 2 was subjected to the ECAP-Conform process with a square cross-section die (at a temperature of 240 °C). This process improved the mechanical properties of CP-Ti grade 2 after one pass, such that both strength and hardness have increased by 35%. The functional properties of dental implants produced from the strengthened titanium and the as-received CP-Ti were compared. It was found that the average grain was reduced from 8.35 μm to 2.35 μm after one pass ECAP-Conform process (i.e. about 72% reduction in grain size). Also, the strength and energy absorption of CP-Ti dental implants made after one pass ECAP-Conform increased by 53% and 139%, respectively.

Tailoring Ti Grade 2 and TNTZ alloy surfaces in a two-step mechanical–chemical modification

ABSTRACT The aim of this work was to improve the surface properties of cp-Ti Grade 2 and β-Ti alloy TNTZ (Ti-29Nb-13Ta-4.6Zr) for biomedical applications. A hybrid surface treatment consisting of shot peening and chemical etching was conducted. Subsequently, the physicochemical properties and topography of the modified surfaces were analysed. Microhardness measurements of the shot-peened samples revealed a great increase in the surface hardness to the similar level as can be achieved for the ultrafine-grained and nanostructured materials. Roughness tests and microscopic observations showed significant topographical differences, depending on the material and modification process involved. Moreover, in this paper we demonstrate the influence of the substrate and treatments on the wettability. Obtained results confirmed that designed hybrid modification of Ti Grade 2 and TNTZ has significant potential for biomedical applications.

A Novel Process to Produce Ti Parts from Powder Metallurgy with Advanced Properties for Aeronautical Applications

Titanium and its alloys have excellent corrosion resistance, heat, and fatigue tolerance, and their strength-to-weight ratio is one of the highest among metals. This combination of properties makes them ideal for aerospace applications; however, high manufacturing costs hinder their widespread use compared to other metals such as aluminum alloys and steels. Powder metallurgy (PM) is a greener and more cost and energy-efficient method for the production of near-net-shape parts compared to traditional ingot metallurgy, especially for titanium parts. In addition, it allows us to synthesize special microstructures, which result in outstanding mechanical properties without the need for alloying elements. The most commonly used Ti alloy is the Ti6Al4V grade 5. This workhorse alloy ensures outstanding mechanical properties, demonstrating a strength which is at least twice that of commercially pure titanium (CP-Ti) grade 2 and comparable to the strength of hardened stainless steels. In the present research, different mixtures of both milled and unmilled Cp-Ti grade 2 powder were utilized using the PM method, aiming to synthesize samples with high mechanical properties comparable to those of high-strength alloys such as Ti6Al4V. The results showed that the fine nanoparticles significantly enhanced the strength of the material, while in several cases the material exceeded the values of the Ti6Al4V alloy. The produced sample exhibited a maximum compressive yield strength (1492 MPa), contained 10 wt.% of fine (milled) particles (average particle size: 3 μm) and was sintered at 900 °C for one hour.

Development of Ti–Al–V alloys for usage as single-axis knee prostheses: evaluation of mechanical, corrosion, and tribocorrosion behaviors

Single-axis knee prosthesis is an artificial biomechanical device that provides motion to amputees without the need for assistance appliances. Besides it is mainly composed of metallic materials, the current commercial materials did not group adequate properties for long-term usage or accessible cost. This study produced and characterized Ti-(10 −x)Al-xV (x = 0, 2, and 4 wt.%) alloys for potential use as single-axis knee prostheses. The samples exhibited a gradual decrease in the density values, with proper chemical mixing of the alloying elements on the micro-scale. The phase composition exhibited a primary α phase with a minor α′ + β phase for the Ti-8Al-2V and Ti-6Al-4V samples. Due to their different atomic radius compared to Ti, the addition of alloying elements changed the cell parameters. Their selected mechanical properties (Young’s modulus, Vickers microhardness, and damping factor) performed better values than the CP-Ti grade 4. The samples also exhibited good corrosion properties against the simulated marine solution. The tribocorrosion resistance of the samples was better than the reference material, with the wear tracks composed of some tribolayers and grooves resulting from adhesive and abrasive wear. The Ti-10Al alloy displayed the best properties and estimated low cost to be used as single-axis knee prostheses.

Fatigue life prediction considering variability for additively manufactured pure titanium clasps.

This study aims to develop a numerical prediction method for the average and standard deviation values of the largely varied fatigue life of additively manufactured commercially pure titanium (CPTi grade 2) clasps. Accordingly, the proposed method is validated by applying it to clasps of different shapes. The Smith-Watson-Topper (SWT) equation and finite element analysis (FEA) were used to predict the average fatigue life. The variability was expressed by a 95% reliability range envelope based on the experimentally determined standard deviation. When predicting the average fatigue life, the previously determined fatigue parameters implemented in the SWT equation were found to be useful after conducting fatigue tests using a displacement-controlled fatigue testing machine. The standard deviation with respect to stroke and fatigue life was determined for each clasp type to predict variability. The proposed prediction method effectively covered the experimental data. Subsequently, the prediction method was applied to clasps of different shapes and validated through fatigue tests using 22 specimens. Finally, the fracture surface was observed using scanning electron microscopy (SEM). Many manufacturing process-induced defects were observed; however, only the surface defects where the maximum tensile stress occurred were crucial. It was confirmed that the fatigue life of additively manufactured pure titanium parts is predictable before the manufacturing process considering its variability by performing only static elasto-plastic FEA. This outcome contributes to the quality assurance of patient-specific clasps without any experimental investigation, reducing total costs and response time.

Development of non-equiatomic Bio-HEAs based on TiZrNbTa-(Mo and Mn)

This study produced non-equiatomic TiNbZrTaMn and TiNbZrTaMo high entropy alloy (HEAs) by argon arc-melting and heat-treated for microstructural homogenization. The phase composition, microstructure, and selected mechanical properties were measured and compared with theoretical predictions. Additionally, electrochemical and cytotoxicity tests evaluated their potential applicability for use as biomaterials. X-ray diffraction measurements patterns showed a single BCC phase for the TiNbZrTaMn and a secondary HCP phase for the TiNbZrTaMo sample. The microstructural analysis revealed the formation of irregular grain boundaries and some lamellae formation, with chemical segregation of the alloying elements at the sub-micro-scale. The samples exhibited elastic modulus (80–110 GPa) closer to CP-Ti grade 2 (100 GPa) and higher Vickers microhardness (450–550 HV) than Ti–6Al–4V alloy (400 HV). The electrochemical and biological tests indicated a superior corrosion resistance against 0.9% NaCl solution compared with commercial metallic biomaterials, with proper cell adhesion and viability of pre-osteoblastic cells and hydrophilic behavior. Altogether, the data indicate that TiNbZrTaMn depicts better applicability potential for being used as a biomaterial in biomedical applications than some commercial materials (SS 316L, CP-Ti grade 2, and Ti–6Al–4V), mainly considering load-bearing orthopedical implants.

Investigating flank face friction during precision micro cutting of commercially pure titanium via plunging tests with diamond grooving tools

This study investigates flank face friction while micro machining commercially pure titanium (cp-Ti grade 2) work material considering size effects. It is important to understand friction phenomena at the tool flank and work material surface since they affect the surface integrity of the machined parts. A single crystal diamond grooving tool is used in machining experiments to reduce the influence of cutting edge radius. In addition, plunging type of cutting experiments were performed to investigate the influence of flank face contact on the machined surface. A friction model which is based on work and tool material properties is proposed to model the contribution of adhesion and deformation of the flank face coefficient of friction. The results show that for the cp-Ti and diamond tool pair, adhesion seems to be the dominant model of friction and also contributes to the size effect. The deformation friction becomes more dominant during the chip formation stage. When cutting edge effect is eliminated, the influences of flank and rake face friction on the size effect are shown.

Effect of Temperature on Electrochemically Assisted Deposition and Bioactivity of CaP Coatings on CpTi Grade 4.

Calcium phosphate (CaP) coatings are able to improve the osseointegration process due to their chemical composition similar to that of bone tissues. Among the methods of producing CaP coatings, the electrochemically assisted deposition (ECAD) is particularly important due to high repeatability and the possibility of deposition at room temperature and neutral pH, which allows for the co-deposition of inorganic and organic components. In this work, the ECAD of CaP coatings from an acetate bath with a Ca:P ratio of 1.67, was developed. The effect of the ECAD conditions on CaP coatings deposited on commercially pure titanium grade 4 (CpTi G4) subjected to sandblasting and autoclaving was presented. The physicochemical characteristics of the ECAD-derived coatings was carried out using SEM, EDS, FTIR, 2D roughness profiles, and amplitude sensitive eddy current method. It was showed that amorphous calcium phosphate (ACP) coatings can be obtained at a potential −1.5 to −10 V for 10 to 60 min at 20 to 70 °C. The thickness and surface roughness of the ACP coatings were an increasing function of potential, time, and temperature. The obtained ACP coatings are a precursor in the process of apatite formation in a simulated body fluid. The optimal ACP coating for use in dentistry was deposited at a potential of −3 V for 30 min at 20 °C.

Biomechanical analyses of one-piece dental implants composed of titanium, zirconia, PEEK, CFR-PEEK, or GFR-PEEK: Stresses, strains, and bone remodeling prediction by the finite element method.

This work aimed to assess the biomechanics, using the finite element method (FEM), of traditional titanium Morse taper (MT) dental implants compared to one-piece implants composed of zirconia, polyetheretherketone (PEEK), carbon fiber-reinforced PEEK (CFR-PEEK), or glass fiber-reinforced PEEK (GFR-PEEK). MT and one-piece dental implants were modeled within a mandibular bone section and loaded on an oblique force using FEM. A MT implant system involving a Ti6Al4V abutment and a cp-Ti grade IV implant was compared to one-piece implants composed of cp-Ti grade IV, zirconia (3Y-TZP), PEEK, CFR-PEEK, or GFR-PEEK. Stress on bone and implants was computed and analyzed while bone remodeling prediction was evaluated considering equivalent strain. In comparison to one-piece implants, the traditional MT implant revealed higher stress peak (112 MPa). The maximum stresses on the one-piece implants reached ~80 MPa, regardless their chemical composition. MT implant induced lower bone stimulus, although excessive bone strain was recorded for PEEK implants. Balanced strain levels were noticed for reinforced PEEK implants of which CFR-PEEK one-piece implants showed proper biomechanical behavior. Balanced strain levels might induce bone remodeling at the peri-implant region while maintaining low risks of mechanical failures. However, the strength of the PEEK-based composite materials is still low for long-term clinical performance.

Effect of Heat Treatment on the Mechanical Properties of a 3 mm Commercially Pure Titanium Plate (CP-Ti Grade 2)

Titanium is seen as a good material for application in many fields due to its compatibility with different environments. However, it remains unclear whether what happens when this material is exposed to certain high temperatures for longer periods of time. The primary objective of this study was to investigate the effect of heat on a 3 mm commercially pure titanium grade 2 plate at a constant temperature of 900°C at different heating times. Three different heating times were employed in this study: 30 minutes for the first period, 60 minutes for the second period, and 90 minutes for the third period. All heated samples were air cooled to room temperature after each heating period. Microhardness, microstructure, tensile strength, and scanning electron microscopy (SEM) tests were performed. All the results were analyzed and compared with the parent sample. It was observed that the heating period influenced microstructural arrangement of the material. The microstructural changes affected negatively the ultimate tensile strength while percentage elongation was improved. The microhardness of the heat treated samples were firstly negatively affected which later jumped and exceeded that of the parent material.

Impact of machining-induced surface defects on the edge formability of commercially pure titanium sheet at room temperature

Despite the good properties of titanium, which have drawn the interest of various industries over the years, one of the major drawbacks of this material is its poor machinability. This has largely been attributed to its low thermal conductivity and elastic modulus. The ability to attain the optimum sheet edge performance during forming is dependent on the quality of the edges produced. Also, the demanding nature of aerospace part design has provoked the interest of both industry and academia to continually explore avenues tailored at enhancing part performance. The sort of edge surface integrity produced for aerospace part fabrication thus becomes a vital consideration in the quest to ensuring prime performance of components. This work seeks to study the influence of different machining-induced surface defects on the sheet edge performance of CP-Ti (grade 2) at room temperature. Hole expansion test was used to assess the edge surface formability of CP-Ti with different machining-induced edge defects. The research found that machining-induced surface defects act as stress concentration sites during the hole expansion test and have a major impact on the material flow. Electro-discharge machined edges were observed to exhibit high edge formability compared to laser and abrasive water jet cut edges due to the impact of machining-induced microstructural changes.

Cobalt–chromium alloys fabricated with four different techniques: Ion release, toxicity of released elements and surface roughness

ObjectiveTo investigate the metal ion release, surface roughness and cytoxicity for Co–Cr alloys produced by different manufacturing techniques before and after heat treatment. In addition, to evaluate if the combination of materials affects the ion release. MethodsFive Co–Cr alloys were included, based on four manufacturing techniques. Commercially pure titanium, CpTi grade 4 and a titanium alloy were included for comparison. The ion release tests involved both Inductive Coupled Plasma Optical Emission Spectrometry and Inductive Coupled Plasma Mass Spectrometry analyses. The surface analysis was conducted with optical interferometry. Cells were indirectly exposed to the materials and cell viability was evaluated with the MTT (3-(4.5-dimethylthiazol-2-yl)-2.5-diphenyltetrazolium bromide) method. ResultsAll alloys showed a decrease of the total ion release when CpTi grade 4 was present. The total ion release decreased over time for all specimens and the highest ion release was observed from the cast and milled Co–Cr alloy in acidic conditions.The cast and laser-melted Co–Cr alloy and the titanium alloy became rougher after heat treatment. All materials were within the limits of cell viability according to standards. SignificanceThe ion release from Co–Cr alloys is influenced by the combination of materials, pH and time. Surface roughness is influenced by heat treatment. Furthermore, both ion release and surface roughness are influenced by the manufacturing technique and the alloy type. The clinical implication needs to be further investigated.

In-vivo study of ultrafine-grained CP-Ti dental implants surface modified by SLActive with excellent wettability

This study investigates the simultaneous effect of substrate nanostructuring by severe plastic deformation and surface modification by SLActive on surface characteristics of CP-Ti grade 2 and evaluates the biocompatibility of it for use as implant material by in-vivo test. SLActive surface modification method is a modified SLA process that includes sandblasting, acid-etching, and cleaning by N2 in a vacuum chamber. To this end, the structure CP-Ti grade 2 was refined by applying the equal channel angular pressing (ECAP) method. Surface morphology, roughness, and wettability of coarse-grained (CG) and ultrafine-grained (UFG) CP-Ti and Ti-6Al-4V were determined after SLActive. It was seen that after surface modification of the samples by SLActive, the excellent wettability with a drop contact angle of about 0° was achieved for SLActived specimens. For the in-vivo test, the implants of each three groups were embedded in the femur of white New Zealand rabbits. In order to assess the osseointegration of implants, histological analysis, and pull-out tests were conducted. Results showed suitable osseointegration between implant and bone for every three groups, but the value of removal torque was higher for UFG-Ti. As is realized UFG-Ti sample surface modified by SLActive could be a suitable choice among the candidates to be used as a material in the manufacturing of dental implants.

Effects of build orientation and sample geometry on the mechanical response of miniature CP-Ti Grade 2 strut samples manufactured by laser powder bed fusion

Additive manufacturing can produce a regular three-dimensional mesh containing tiny interconnected wires/struts that form a porous structure. It is reasonable to assume that the properties of these single wires/struts will affect the performance of each unit-cell contained within the porous structure and thereby affect the mechanical properties of the whole porous structure. The effects of strut geometry and build orientation on resulting mechanical properties are examined in this study. Laser powder bed fusion was used to manufacture single strut samples of CP-Ti Grade 2 in the vertical and horizontal orientations with cross-sectional areas ranging from 0.07 mm2 to 2.3 mm2. For samples with cross-sectional areas smaller than 1.5 mm2, the difference in yield strength between the vertical and the horizontal build orientations was 79%, consistent with differences in microstructure scale in these orientations. Build orientation effects were much less pronounced in larger samples where the microstructural scale and features were similar. The presence of surface roughness and process-induced porosity contributed to the significant differences in ductility exhibited in the different orientations. The results indicate that build orientation effects may be significant for as-deposited surfaces and should be considered when designing porous structures consisting of thin struts since these will likely be used with as-deposited surface roughness.