English 
Español 
हिन्दी 
العربية 
Português do Brasil 
Русский 
日本語 
Deutsch 
한국어 
Français 
Türkçe 
Polski 
Tiếng Việt 
Italiano 
简体中文 Tool wear is a critical bottleneck restricting the machining efficiency, quality, and cost-effectiveness of Ti6Al4V, a key titanium alloy widely used in the aerospace industry. Characterized by poor thermal conductivity, high chemical activity, and low elastic modulus, Ti6Al4V tends to generate excessive cutting heat during machining, which significantly accelerates tool wear and even leads to premature tool failure. Given that excessive tool wear directly limits the cutting speed of titanium alloys and increases the production cost of components, exploring the wear mechanisms and morphological characteristics of cemented carbide tools under Ti6Al4V cutting conditions is of great practical engineering value.
Test Conditions
Workpiece Material
Ti6Al4V possesses an α+β dual-phase microstructure. Its key mechanical properties are listed as follows: tensile strength σb＞980 MPa, yield strength σ0.2＞830 MPa, elongation δ＞13%, elastic modulus E＞115 GPa, and hardness of 37 HRC. Cylindrical Ti6Al4V bars with a length of 350 mm and a diameter of 140 mm are adopted in the test. Table 1 presents its chemical composition.
Tool Material and Geometric Parameters
Conventional theories suggest that YT and YW series cemented carbides containing TiC and TaC are unsuitable for titanium alloy cutting, while YG series tools are widely applied in actual production. This convention stems from the strong chemical affinity between titanium in workpieces and tool substrates. Cutting speed exerts a prominent impact on wear behaviors, and high-speed cutting triggers obvious differences in tool wear mechanisms compared with low-speed conditions.
To systematically clarify the wear behaviors of cemented carbide tools across speed ranges, three representative tool grades YT15, YW2 and YG8 are selected for controlled comparison, with identical insert profiles and geometric angles. Table 2 to Table 4 illustrate their alloy compositions, elemental mass fractions and mechanical properties respectively.
The tool holder model is 90W25-3K13. Key geometric parameters of inserts are set as: rake angle γ₀=6°, flank angle α₀=6°, minor flank angle α₀’=7°, chamfer width 0.2 mm, chip groove width 5 mm, nose radius 0.5 mm, and major cutting edge angle kᵣ=90° after installation. Figure 1 displays the tool holder and inserts used in the experiment.
Cutting Test Scheme
All cutting experiments are carried out on a CAK6150 CNC lathe, with cutting speed adjusted by regulating spindle speed. Inserts are disassembled at fixed cutting intervals to observe macro wear morphologies and flank wear loss via a VHX-1000 ultra-depth-of-field 3D microscope. A SM-6360LA scanning electron microscope is adopted for micro wear observation, and energy dispersive spectroscopy (EDS) is used for elemental analysis on worn tool surfaces.
A single-factor method is applied to analyze the correlation between cutting speed and tool wear. Dry cutting tests are performed at low, medium-high and high speeds. Fixed cutting parameters: cutting speed v=48 m/min, 71 m/min, 100 m/min; cutting depth a<sub>p</sub>=0.3 mm; feed rate f=0.2 mm/r.
Test Results and Analysis
Tool Wear Morphologies
Primary tool wear forms include rake face wear, flank wear and boundary wear, which usually occur simultaneously. Titanium alloy machining involves severe friction between tools, workpieces and chips. Extreme contact pressure and cutting heat induce multi-region wear, and the low elastic modulus of titanium alloys causes prominent springback of machined surfaces, further aggravating minor flank wear. Figure 2 characterizes typical wear features of cemented carbide tools when cutting Ti6Al4V.
Crater wear dominates the rake face (Fig. 2a), formed by coupled friction, high temperature and high pressure during chip flowing. Continuous contact and friction between the major flank and machined surfaces generate high pressure and heat, resulting in major flank wear (Fig. 2b).
Severe surface springback of finished workpieces intensifies friction on the minor flank, leading to minor flank wear (Fig. 2c). Chip adhesion can also be observed near the tool nose and minor flank (Fig. 2d). Comparative analysis of Fig. 2b and 2c indicates that the minor flank suffers wider wear coverage and larger wear loss. Such differences are attributed to workpiece springback and chip adhesion, which intensify extrusion and friction on the minor flank.
Tool Wear Mechanism under Low-speed Cutting
Figure 3 to Figure 6 show SEM micrographs and EDS results of minor flank wear of cemented carbide tools under low-speed cutting. Adhesive deposits can be clearly observed on worn tool surfaces (Fig. 3). With high chemical activity and strong material affinity, Ti6Al4V tends to form adhesive chip layers on tool substrates. Peeling of adhered particles during continuous cutting eventually causes adhesive wear.
Table 2 lists the alloy composition of three tools, and corresponding elemental mass fractions are calculated and summarized in Table 3. Table 5 records the main elemental contents on worn tool surfaces after low-speed cutting, derived from EDS data in Fig. 4 to Fig. 6.
Comparative analysis of Table 3 and Table 5 reveals abundant Ti, Al and V elements on all tool surfaces after low-speed machining, accompanied by a sharp decline in W content. W and Co elements are undetectable on partial detection points of YG8 and YW2 tools, fully covered by adhered workpiece materials. Given the 1 μm maximum detection depth of EDS probes, the thickness of titanium alloy adhesion layers exceeds 1 μm. In summary, strong material affinity leads to widespread adhesion on all three tools during low-speed Ti6Al4V cutting. YW2 and YG8 suffer severe adhesion while YT15 shows mild adhesion, proving adhesive wear as the dominant tool wear mode at low speeds.
Tool Wear Mechanism under High-speed Cutting
Extreme cutting heat in high-speed machining promotes chemical reactions between oxygen and cemented carbide components such as WC, TiC and Co, forming low-hardness oxide films. Limited air circulation in cutting zones confines oxide film formation to wear edges. Repeated friction from scale layers, work-hardened surfaces and hard inclusions damages oxide films and induces flank oxidation wear, which evolves into obvious wear grooves under excessive material loss (Fig. 7).
EDS analysis (Fig. 8~10) and data comparison between Table 3 and Table 6 verify widespread oxygen distribution on worn flanks, with the maximum O content reaching 29.32%. This confirms severe oxidation wear driven by high cutting temperature.
Data comparison between Table 5 and Table 6 demonstrates that high-speed cutting reduces Ti content and increases W content on YT15 and YW2 inserts, effectively suppressing adhesive wear. For YW2 tools, drastic growth of C and O elements originates from high-temperature decomposition of WC and TaC as well as oxidation reactions. YT15 presents rising O content and stable C content, indicating dominant oxidation wear and weak diffusion wear. In contrast, YG8 still retains a high Ti content of 62.88% with rich Al and V residues. Although its W content increases slightly, it remains far lower than the original level. Severe adhesion persists on YG8, with adhesive wear remaining dominant and slight diffusion and oxidation wear.
In conclusion, YG8 is still governed by adhesive wear in high-speed Ti6Al4V cutting. The dominant wear modes of YT15 and YW2 transform from adhesive wear to diffusion and oxidation wear, with YW2 exhibiting the most significant high-temperature diffusion and oxidation behaviors.
Effects of Cutting Speed on Tool Wear
Cutting speed acts as the core factor affecting tool wear in Ti6Al4V machining (Fig. 11). Increased cutting speed accelerates minor flank wear and shortens tool service life for all three tool grades:
- At 48 m/min: YT15 suffers the fastest wear, while YW2 and YG8 deliver comparable and superior wear resistance. Severe adhesion on YW2 and YG8 excludes material affinity as the core cause for rapid YT15 failure. Instead, the low content of Co binder phase reduces substrate toughness and strength, causing material peeling after workpiece adhesion.
- At 100 m/min: YG8 wears most rapidly, followed by YT15, and YW2 performs optimally. High temperature softens the Co phase of YG8 and weakens structural stability, accelerating its adhesive wear. YT15 shows weakened adhesion and increased diffusion & oxidation wear. YW2 achieves balanced multiple wear modes, and TaC additives enhance its high-temperature structural strength.
- At 71 m/min: The wear rate ranks as YT15＞YG8＞YW2. Moderate cutting temperature reduces Co phase degradation, making low-toughness YT15 vulnerable to damage. Partial failure of the Co binder phase aggravates YG8 wear, while weakened adhesion and enhanced high-temperature resistance enable YW2 to maintain stable performance.
Conclusions
(1) Adhesive wear dominates the failure of all three tools under low-speed cutting. Insufficient Co binder content accelerates local material shedding and tool wear.
(2) YG8 remains dominated by adhesive wear in high-speed cutting. YT15 undergoes combined adhesive, diffusion and oxidation wear, while YW2 presents balanced multiple wear mechanisms. High-temperature failure of the Co binder phase is the key inducement for comprehensive tool wear.
(3) YW series cemented carbides are recommended as ideal matrix materials for developing high-performance coated and fine-grained tools for high-speed titanium alloy cutting.
(4) From the perspective of cost efficiency, YG series tools are preferred for low-speed titanium alloy machining, and YW series tools are more suitable for high-speed cutting conditions.
