ECAP of commercially pure titanium: A review

Abstract

REVIEWECAP has emerged as an attractive technique in last two decades and is gaining as a potential route for industrial production. Though it is a well known the technique, for the sake of completeness a brief introduction about ECAP process is given.In the ECAP process a well lubricated billet is pressed in a die that contains two channels, equal in cross section, intersecting at an angle called die channel angle. The material is subjected to shear deformation at the intersection plane. Since the process is capable of maintaining the net dimensions of the work piece, repetitive extrusion is possible, provided that the material has sufficient ductility, to withstand heavy deformations. The multiple ECAP passes make it possible to rotate the billet around its longitudinal axis between the passes, creating different routes.Conventionally ECAP has been classified into four routes based on the rotation of billet between each passes with reference to its longitudinal axis as (i) Route A, no rotation (ii) Route B A , rotating 90 0 in opposite directions, (iii) Route B c , rotating 90 0 in the same direction and (iv) Route C, rotating 180 0 . Figure 1 schematically illustrates the four processing routes of ECAP.The shear planes in extrusion axis (X direction), Perpendicular axes (Y and Z direction) tend to rotate based on the channel angle and processing route and hence the properties tend to change accordingly. The shearing plane on the three directions and in four routes is schematically given in Fig. 2.Usually, the billets are rotated with reference to X axis only. The rotation of the samples in X plane is more effective as compared to Y and Z axis based on the shearing patterns which can be understood from Fig. 2. ABSTRACTEqual Channel Angular Extrusion (ECAE) also called as Equal Channel Angular Pressing (ECAP) is an emerging mechanical or thermo mechanical method for synthesis of bulk ultra fine grained or nano materials. The uniqueness of ECAP is that the fine grains are obtained without changing any of the dimensions of the sample. The grain refinement increases the strength of CP-Ti to the strength levels of Ti-6Al-4V, a commonly used material for bio implants. Though Ti-6Al-4V alloys satisfy the biomedical requirements, the Al and V are toxic to human tissue. ECAP is an attracting technique for strengthening commercially pure titanium (CP-Ti) to a level of Ti-6Al-4V since CP-Ti has better compatibility for bio medical applications. Hence, the research is focused on ECAP of CPTi. This overview mainly focuses on the mechanical properties, corrosion resistance, wear resistance, fatigue resistance and the influence of external and internal parameters on the properties of ECAPed CP-Ti. It also highlights the methods employed for increasing the deformability of CP-Ti. Finally, the suitability of ECAP for industrial production is also discussed. The state of the art in this field is encouraging and showing positive signs of commercializing ECAP of CP-Ti in the near future.

Recent Advances in the Equal Channel Angular Pressing of Metallic Materials

“…For example, Ag, which is also an FCC metal, is more prone to twinning deformation, while Cu and Al are prone to slip deformation because of the low fault energy of Ag. HCP metals prefer c/a-based twinning due to the lack of slip systems [20].…”

“…For example, Ag, which is also an FCC metal, is more prone to twinning deformation, while Cu and Al are prone to slip deformation because of the low fault energy of Ag. HCP metals prefer c/a-based twinning due to the lack of slip systems [20]. In the initial stage of compression deformation, twinning dominates the deformation mechanism due to the larger grain size, and as the strain increases, the grain size is refined and the twinning decreases [145].…”

“…Many scholars have used this method to alter the microstructure and improve the mechanical properties of non-ferrous metals including Al, Ti, Mg, Cu, and their alloys [17,18]. Previous studies have shown that the improvement of material properties by ECAP is affected by many factors, such as passes, temperature, routes, back pressures, channel angle, etc., and the grain size can be effectively reduced by controlling the processing parameters [14,17,19,20]. The strain distribution of aluminum after different channel angles, curvature angles, and passes was simulated by the finite element method.…”

“…The strain uniformity was quantitatively studied by using a non-uniformity index and standard deviation, and the best suggestions for die parameters were given. When the channel angle is obtuse, the effective strain decreases with the increase of the angle; When the channel angle is acute, the deformation is more uneven and complex; When the channel angle is a right angle, the effective change is uniform [20,21]. Figure 1 schematically shows the ECAP process and schematic diagram of different routes.…”

Impact of Equal Channel Angular Pressing on Mechanical Behavior and Corrosion Resistance of Hot-Rolled Ti-2Fe-0.1B Alloy

“…In recent decades, severe plastic deformation (SPD) has been used to produce ultrafine-grained (UFG)/nanostructure (NS) materials and improve their physical and chemical properties [ 10 , 11 , 12 ]. Among them, equal channel angular pressing (ECAP) is one of the most effective methods which can be used to fabricated bulk UFG materials and has great industrial application potential [ 13 , 14 ]. Many UFG metals including Titanium fabricated by ECAP exhibit improved mechanical properties, for example, the high strength of 627 MPa and 1435 MPa could be achieved after ECAP for Grade 2 [ 15 ] and Grade 5 [ 16 ] Titanium alloys respectively.…”