Research Papers

Phase Dependent Tool Wear in Turning Ti-6Al-4V Using Polycrystalline Diamond and Carbide Inserts

[+] Author and Article Information
David J. Schrock, Patrick Kwon

Mechanical Engineering,
Michigan State University,
East Lansing, MI 48823

Di Kang, Thomas R. Bieler

Chemical Engineering and Material Science,
Michigan State University,
East Lansing, MI 48823

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING. Manuscript received February 11, 2013; final manuscript received May 8, 2014; published online June 2, 2014. Assoc. Editor: Burak Ozdoganlar.

J. Manuf. Sci. Eng 136(4), 041018 (Jun 02, 2014) (8 pages) Paper No: MANU-13-1060; doi: 10.1115/1.4027674 History: Received February 11, 2013; Revised May 08, 2014

Tool wear of polycrystalline diamond inserts was analyzed in turning experiments on Ti-6Al-4V. Evidence of phase transformation in turning titanium work material is presented and its impact on tool wear is discussed. Confocal laser scanning microscopy was used to analyze the rake face of the turning inserts. At cutting speed of 61 m/min, the rake face exhibited scalloped-shaped, fractured wear, characteristic of typical attrition wear. At cutting speed of 122 m/min, a smooth crater was observed, which is a typical characteristic of diffusion/dissolution wear. At the cutting speed of 91 m/min, the wear features were a combination of those observed at speeds of 61 m/min and 122 m/min. A comparison of the wear on the polycrystalline diamond (PCD) tools to that of WC-6Co from our earlier work is also discussed. Microstructural analysis of the of both the undeformed work material and the chip using electron-backscatter diffraction provided evidence to support the phase transformation. Temperature estimates on the rake face of the tool previously extracted from Finite Element Method (FEM) support the possibility of phase transformation at the high cutting speed tested. The difference in the wear pattern was also linked to the extent of recrystallization in the titanium work material. At 61 m/min there was more alpha phase in the work material without much recrystallization, which generated uneven scalloped wear. At 122 m/min, phase transformation of the existing alpha phase to the beta phase in the work material and recrystallization increased the dissolution/diffusion wear process.

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Fig. 1

Schematic of the metallurgical mounting process of the as received Ti-6Al-4V work material

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Fig. 2

EBSD configuration, where the electron beam directed by the computer interacts with a sample that is tilted 70 deg. Backscattered electrons form diffraction patterns on the EBSD camera, and are processed by the computer that is connected to it [11]. The Euler angle coordinate system is Z is the sample normal direction, and X is down.

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Fig. 3

The evolution of wear on the rake face of the PCD insert after machining at 61 m/min, 91 m/min, and 122 m/min for the indicated cutting times

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Fig. 4

The evolution of wear on the rake face of the WC-6Co insert after machining at 61 m/min for 6 min and 12 min (top row) and 122 m/min for 30 s and 2 min (bottom row) shown at 20x magnification [7]

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Fig. 5

Images showing the rake surface of a typical PCD insert at 10x magnification after machining Ti-64 at 61 m/min and 122 m/min before and after etching. Note the difference in adhered Ti on the rake face.

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Fig. 6

EBSD map (step size 1.7 μm) of the microstructure of the work material viewed from the −1 −1 1 direction (presented in red) based on the coordinate system shown (see also Fig. 1)

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Fig. 7

Schematic detailing the relationship between the −1,−1,1 direction in the TSL coordinate system and the shear plane normal in the physical coordinate system

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Fig. 8

EBSD map of the microstructure in Fig. 7 partitioned to show only grains with basal planes oriented within 30 deg of −1 −1 1, on which a high shear strain was imposed

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Fig. 9

A backscatter image of a section of the Ti-64 chip after cutting at 61 m/min using a PCD insert with an OIM map of the microstructure; EBSD pattern quality map with grain boundary segments having a 60 deg, 85 deg, and 90 deg misorientations in blue, yellow, and red, respectively, and a normal direction inverse pole figure map

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Fig. 10

A close up of a portion of the microstructure of the chip in Fig. 11 showing the line along which the misorientation profile was taken indicated by the white arrow in Fig. 9, where 85 deg twin misorientations about a common 〈a〉 axis are evident

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Fig. 11

Misorientation versus distance along the line indicated by the red arrow in Fig. 11. Note the oscillating 90 misorientations strongly suggesting phase change in the Ti during chip formation.

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Fig. 12

EBSD pattern quality map with grain boundary segments having a 60 deg, 85 deg, and 90 deg misorientations in blue, yellow, and red, respectively, and a normal direction inverse pole figure map of the microstructure of a Ti-64 chip after cutting at 122 m/min using a PCD insert

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Fig. 13

Plot of misorientation versus distance along the line intersecting grains shown in Fig. 12

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Fig. 14

Ti-6Al-V phase diagram [11] showing the Ti-6Al-4V composition line modified with added points to show the equilibrium composition at estimated cutting temperature for each cutting speed

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Fig. 15

Temperature-Pressure phase diagram for Ti from [14]. The phase diagram shows a reduction in the beta transus temperature with increased pressure.




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