Experimental Study on Titanium Coating Carbide Drill Cutting Nickel-Base Superalloy

Abstract

A nickel-base superalloy drilling comparison test was carried out with a carbide drill of the Chinese brand YG10, which was selected and coated with TiN coating, AlTiN coating and TiAlSiN coating. Analysis of drill life, drilling force, drilling temperature, drill wear and machined surface quality were carried out. It can be seen that both TiN coating and AlTiN coating can prolong the tool life of the carbide drill YG10 when drilling nickel-base superalloy GH4169. In contrast, the TiAlSiN-coated drill has poor hardness and is easy worn, which is not suitable for processing nickel-base superalloy which has high hardness and strength. Adhesive wear is the main form of coated drill wear. As the coated drill number of drilling holes increases, the adhesion increases. Coated drills can reduce the machined surface roughness of a workpiece and improve the machined quality.

1. Introduction

Nickel-base superalloy GH4169 contains a lot of alloying elements with high melting points, high activation energy and stable structure. With the characteristics of high strength, high hardness, high toughness and high temperature resistance, it is widely used in engine components that need to withstand high temperatures in aerospace, nuclear energy, petroleum and other industrial fields, such as aero-engine blades, combustion chambers and turbine disks [1,2,3,4,5]. However, its thermal conductivity is extremely low. Especially in the drilling process, the drill will rub strongly with the workpiece, and it is not easy to dissipate its heat. Due to the high temperature in the cutting zone over qa long duration, the drill life is extremely short.

Sun Jinliang [6] carried out the test of a high-cobalt high-speed steel drill and a carbide drill drilling nickel-base superalloy. According to the results, the high-cobalt high-speed steel drill lost its machining capability when the drilling depth was about 5–6 mm. At a machining depth of 5 mm, the carbide drill could process up to 20 holes. Eckstein M [7] used a carbide twist drill to machine 8.5 mm diameter holes. After machining 24 holes, the rake wear reached the failure criterion. Kannan S [8] used a carbide twist drill with internal coolant to machine a hole with a diameter of 12.99 mm. Flank wear affected machined quality after machining 40 holes. Li, H. [9] studied the drilling performance of an uncoated carbide drill YG10 and CrAlYN-coated drill dry-drilling nickel-base superalloy. The CrAlYN coating was shown to improve drilling performance. It can be seen that nickel-base superalloy has poor drilling performance and shortens tool life. Therefore, research on drilling performance is of great significance for improving the durability of cutting tools.

In the drilling process, the coating of the cutting tool can combine the excellent performance of the cutting tool base and the coating material, which maintains the good toughness and high strength of the base, and the high hardness, high wear resistance and low friction coefficient of the coating. Therefore, the drilling performance of the cutting tool is greatly improved [10,11,12]. The uncoated carbide drill of Chinese grade YG10 was coated with TiN, AlTiN, and TiAlSiN, respectively, by PVD (Physical Vapor Deposition). The green drilling test of nickel-base superalloy GH4169 was carried out under both conventional dry drilling and LCO₂ cooling. In addition, drilling force, drilling temperature, drill wear and machined surface quality were analyzed. The purpose of this study is to improve the drilling performance and tool life of drilling nickel-base superalloy.

2. Materials and Methods

(1)

Workpiece material

The test material is a nickel-base superalloy GH4169 sheet, which corresponds to Inconel 718 in US. The thickness of the workpiece is 18 mm. See

Table 1. Chemical composition of nickel-base superalloy GH4169.

Element	Ni	Cr	Nb	Mo	Ti	C	Si	Mn	B	Fe
Mass/%	51.75	17	5.15	2.93	1.07	0.042	0.21	0.03	0.006	Bal

for chemical composition [13] and

Table 2. Material properties of workpiece.

Density/(kg/m3)	Poisson’s Ratio μ	Thermal Conductivity/(W/m·K)	Specific Heat Capacity/(J/kg·°C)	Modulus of Elasticity/GPa
8240	0.3	14.7	435	199.9
Elongation/%	Reduction of section/%	Tensile strength/GPa	Impact Toughness/(MJ/m3)	Yield Strength/MPa
24	40	1430	348	1110

for material properties [14].

(2)

Drill

The test uses carbide drill with Chinese grade YG10 made by GSOK. Common data include diameter of 6 mm, length of 55 mm, apex angle of 118°, and helix angle of 30°. See

Table 3. Chemical composition of carbide drill YG10.

Cutting Tool Serial No.	Element Mass Fraction(%)
	W	Co	C
YG10	84	10	6

for chemical composition and

Table 4. Mechanical properties of carbide drill YG10.

Cutting Tool Serial No.	Mechanical Properties
	Density g/cm−3	Hardness HRA	Bending Strength MPa	Compressive Strength MPa	Elastic Modulus GPa	Impact Toughness J/cm−2
YG10	14.7	88.5	2700	4700	585	2.8

for mechanical properties.

In cooperation with Luoyang Our Materials Technology Co., LTD., the selected YG10 carbide drills are, respectively, coated with TiN, AlTiN and TiAlSiN coatings using DC arc plasma spraying equipment., respectively. The actual drill is shown in Figure 1, and the chemical composition is shown in

Table 5. Chemical composition of YG10 carbide drill.

Coating Type		Element Mass Fraction (Wt%)
	Ti	Al	Si	N
TiN	69.14	-	-	30.86
AlTiN	22.78	47.37	-	29.86
TiAlSiN	23.84	41.24	6.36	28.56

.

Through the comparative test and analysis of coated drill and uncoated drill, it is studied to improve the drilling performance of carbide drill green cutting nickel-base superalloy.

(3)

Test condition

The device for drilling test is shown in Figure 2. The test machine tool is the XK714F CNC programming five-axis milling machine produced by Hanchuan CNC Machine Tool Company (Hanzhong, China), with a maximum speed of 3000 rpm. During the drilling process, the force sensor LH-SZ-02F developed by Shanghai Liheng Company (Shanghai, China) is used to measure the drilling force, with a stroke of 0–5000 N. The computer is connected to the NI data acquisition instrument through a signal amplifier. The FLIRA315 online infrared thermal imaging system is used to measure the temperature of the drilling area, which is connected with the computer to output the temperature change curve in real time.

In order to avoid the randomness of experimental results, each group of experiments was repeated three times, and the average was taken. During drilling, the drill is removed after every 5 holes. Through a 30x tool microscope, cutting tool appearance and wear amount are observed. After the test, a scanning electron microscope (SEM) made in the Czech model Quanta 250 (FEI Company, Hillsboro, OR, USA) is used to observe the drill wear appearance. The elemental composition of the drill wear area is analyzed by the supporting Energy Dispersive Analysis of X(EDAX) with the SEM.

3. Test Results and Analysis

3.1. Drill Life

This test was carried out with a feed rate of 0.04 mm/r and a drilling depth of 6 mm, the drilling of uncoated drill, TiN-coated drill, AlTiN-coated drill and TiAlSiN-coated drill were compared at different drilling speeds.

The number of drilling holes is used to reflect tool life. The drill wear condition was observed by the tool display micromirror after each continuous drilling of 5 holes. If the outer edge of the drill main cutting edge (VB_c) wears up to 0.3 mm, it will fail. Figure 3 shows the tool life of an uncoated drill, a TiN-coated drill, AlTiN-coated drill, and TiAlSiN-coated drill at different drilling speeds.

According to Figure 3, the tool life of the uncoated drill, the TiN-coated drill, and the AlTiN-coated drill is the longest when the drilling speed is 15 m/min, which shortens as the drilling speed increases.

The maximum number of drilling holes for the TiAlSiN coated drill is 10 at the speeds of 20 m/min and 25 m/min. Therefore, the TiAlSiN coating does not prolong the tool life; in fact, it is much shorter than the tool life of the uncoated drill under the same drilling. The TiAlSiN coating is not suitable here.

When the drilling speed is 15 m/min, the tool life of TiN coated drill is 1.67 times that of uncoated drill, and the tool life of the AlTiN-coated drill is 1.83 times that of uncoated drill and 1.1 times that of TiN coated drill. Therefore, it can be concluded that the suitable coating can prolong tool life. In addition, the performance of the AlTiN coating is better than that of TiN coating.

Since the number of drilling holes in the TiAlSiN-coated drill is too small when the drilling speed is 30 m/min, this study mainly analyzes the drilling force and drilling temperature with other coated drills.

3.2. Drilling Force

The average force of the 5th hole in the plateau stage after each drilling of 5 holes is compared by the selected core, as shown in Figure 4. Among them, Figure 4 shows the comparison of drilling force at different drilling speeds. The drilling force of the uncoated drill is relatively large, which increases as the number of drilling holes increases, especially when the drilling speed is 20 m/min. The drilling force of the TiN-coated drill does not change greatly with the increase of drilling speed, but is basically stable at about 600 N. Then, the drilling force increases significantly before reaching failure. The drilling force of the AlTiN coated drill is smaller than that of the uncoated drill and the TiN-coated drill. In addition, it decreases slightly with the increase of drilling speed, and is basically stable at around 600 N. Through data analysis, it can be found that the drilling force of the uncoated drill is significantly reduced after the TiN-coated and the AlTiN-coated drill, because the coating reduces the friction force of the drill.

3.3. Drilling Temperature

The thermal imager takes the maximum temperature in the measured area, as shown in Figure 5.

The maximum temperature of the 5th hole after drilling 5 holes is recorded and plotted. Figure 6 shows the drilling temperature curves under different working conditions. Figure 6 shows the temperature profiles under different drilling speeds. When the drilling speed is 15 m/min, the drill life of the uncoated drill, the TiN-coated drill, and the AlTiN-coated drill is the longest. At this time, the drilling temperature is basically stable. The drilling temperature of the AlTiN-coated drill is the highest, around 250 °C. The drilling temperature of the TiN-coated drill is second, around 230 °C. The drilling temperature of the uncoated drill is the lowest, around 210 °C.

When the drilling speed is 20 m/min, the drill life of the AlTiN-coated drill is longer. The temperature with the AlTiN-coated drill is basically stable and around 270 °C. The uncoated drill and the TiN-coated drill are broken soon under these conditions, then the temperatures rise quickly. Through data analysis, it can be found that the drilling temperature of the uncoated drill increases significantly after the TiN-coated and AlTiN-coated are applied, because the protective effect of the coating makes the drilling temperature difficult to emit. In addition, the temperature isolation function of the coating also protects the drill base.

3.4. The Wear Mechanism of Coated Drill

At drilling speeds of 15 m/min and 20 m/min, the drill life of the AlTiN-coated drill is significantly longer than that of the TiN-coated drill, as shown in Figure 7 for the drills’ wear morphology. Figure 7a shows the appearance of the TiN-coated drill after drilling 50 holes at the speed of 15 m/min. Damage and wear on the outer edge of the main rear cutter face reach the failure standard. Figure 7b shows the appearance of the TiN-coated drill after drilling 30 holes at the speed of 20 m/min. The outer edge of the back tool surface becomes purple because of excessive temperature. Figure 7c shows the appearance of the AlTiN-coated drill after drilling 55 holes at the speed of 15 m/min. The wear on the outer edge of the main rear cutter face reaches the failure standard. Figure 7d shows the appearance of the AlTiN-coated drill after drilling 45 holes at the speed of 20 m/min. The drill life of the AlTiN-coated drill is significantly longer than that of the TiN-coated drill at the speed of 20 m/min.

Among the several coatings tested above, drilling with an AlTiN-coated drill has the best performance, and its wear appearance by SEM when the drilling speed is 15 m/min is shown in Figure 8. Figure 8 shows the main flank appearance of the AlTiN-coated drill after drilling 55 holes. The coating on the drill’s main cutting edge is removed, but the unremoved coating still protects the drill base.

The EDAX spectrometer equipped with SEM is used to analyze the chemical composition of the main cutting edge, and the results are shown in Figure 9. The composition of the original drill is only W, Co, and C. However, it can be found that Ni, Fe, and Cr, which have a large proportion of components in the main cutting edge, are all nickel-base superalloy material elements, which indicates that the adhesion has occurred.

3.5. Roughness of Workpiece Machined Surface

This test measured the average roughness (Ra) of the inner wall of the drilled hole at the longest tool life of the uncoated drill, the TiN-coated and the AlTiN-coated drill. The comparison chart is shown in Figure 10. It can be seen that the coating reduces the machined surface roughness and improves the machined quality. The AlTiN-coated drill is slightly better than the TiN-coated drill.

4. Conclusions

A drilling nickel-base superalloy comparative test is carried out with an uncoated carbide drill and a TiN, an AlTiN, and a TiAlSiN-coated drill, and the drill life, drilling force, drilling temperature, wear appearance and wear curve are analyzed. The following conclusions are drawn.

(1)

TiN coating and AlTiN coating can prolong the tool life of the carbide drill YG10 when drilling nickel-base superalloy GH4169. The TiN coating can prolong tool life by 1.67 times, while the AlTiN coating can prolong tool life by 1.83 times.

(2)

The friction force of TiAlSiN coating is small, but the hardness is poor, which leads to it being easily worn. Therefore, it is not suitable for the processing of nickel-base superalloy with high hardness and high strength.

(3)

Adhesive wear is the main form of coating drill failure form. As the number of drilling holes of the coated drill increases, the adhesion becomes heavier and the drilling force and temperature increase.

(4)

Coating can reduce the roughness of the machined surface of carbide drill drilling nickel-base superalloy and improve the machined quality. The AlTiN-coated drill is slightly better than the TiN coated drill.