Basic ionic liquid as catalyst and surfactant: green synthesis of quinazolinone in aqueous media

Article abstract of DOI:10.1039/C8RA06378H

Basic imidazolium-based ionic liquids not only possess the extraordinary physicochemical properties of ionic liquids, but also have excellent basicity and surfactivity. 1-Propyl-3-alkylimidazole hydroxide ionic liquids ([PRIm][OH]) were synthesized and their catalytic and surfactant behavior were studied in this work. [PRIm][OH] owned excellent surfactivity, and their alkyl chains and ion pairs benefit hydrophobicity and hydrophilicity respectively. The surfactivity of [PRIm][OH] increased with increasing alkyl chain length. [PRIm][OH] showed better catalytic performance than NaOH in the condensation of 2-aminobenzonitrile with cyclohexanone in aqueous medium, and the catalytic performance was well coincident with their surfactant behavior. [PRIm][OH] could decrease the interfacial tension of solvent effectively and form micelles in water. The formed micelles could solubilise more reactants into water and effectively increase the chance of contact between reactants and catalytic active sites. The catalyst dosage obviously affected catalytic performance. The catalytic system is a promising recyclable system.

Full text of DOI:10.1039/C8RA06378H

metals
Article
Effect of Quenching Temperature on Microstructure
and Rolling Contact Fatigue Behavior of
17Cr2Ni2MoVNb Steel
Yalong Zhang 1,2,3, Shengguan Qu 1,2,3,
and Xiaoqiang Li 1,2,3
*
, Fuqiang Lai 1,2,3, Haidi Qin 1,2,3, Liman Huang 1,2,3
1
Guangdong Key Laboratory for Advanced Metallic Materials Processing,
South China University of Technology, Guangzhou 510640, China; zhanglong_china@126.com (Y.Z.);
lfq0623@163.com (F.L.); 15914445865@163.com (H.Q.); nn_huangliman@163.com (L.H.);
lixq@scut.edu.cn (X.L.)
National Engineering Research Center of Near-Net-Shape Forming for Metallic Materials,
Guangzhou 510640, China
2
3
School of Mechanical and Automotive Engineering, South China University of Technology,
Guangzhou 510640, China
*
Correspondence: qusg@scut.edu.cn; Tel.: +86-020-8711-1983
ꢀꢁꢂꢀꢃꢄꢅꢆꢇ
ꢀꢁꢂꢃꢄꢅꢆ
Received: 28 August 2018; Accepted: 17 September 2018; Published: 19 September 2018
Abstract: 17Cr2Ni2MoVNb steel is a new type of gear steel in the automotive industry; the rolling
contact fatigue behavior is not well documented. In this study, some microscopic analysis methods
(optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope
(TEM), X-ray diffractometer (XRD), and energy dispersive X-ray analysis (EDS)) were used to
characterize material microstructure and damage surface. In addition, rolling contact fatigue behavior
was evaluated by Weibull curve. The results show that the size of austenite grain increased while the
quenching temperature increased. Moreover, the samples with a quenching temperature of 1000 ◦C
exhibited the maximum mean life of 7.33
×
105 cycles. In addition, the failure mode of quenched at
900 ◦C and 1100 ◦C were delamination, and pitting was the main failure mode of 1000 ◦C.
Keywords: 17Cr2Ni2MoVNb; microstructure; quenching temperature; rolling contact fatigue
1. Introduction
Rolling contact fatigue (RCF) is a typical failure mode in the application of gears. Surface damage
is a very complex phenomenon and the contact fatigue plays a fundamental role in the damage
process [
surface roughness, and mechanical properties of materials [
on different heat treatment processes to improve mechanical properties in Fe-based alloys [
Long [ ] investigated the effect of quenching temperature on martensite multi-level microstructure
1
]. The fatigue damages are influenced by various factors, including the lubrication oil,
]. Numerous studies have focused
].
2–5
6,7
8
and properties of strength and toughness in 20CrNi2Mo steel and found that the impact toughness
and fracture toughness increase by 32.4% and 27.8% with increasing of the quenching temperature,
respectively. The early work by Matlock [9] indicated that the grain size is the most important factor
affecting fatigue behaviors. Ma [10] determined the fatigue resistance is affected by plastic deformation
under different slip ratio conditions. Wang [11] explored a coupling relationship between fatigue
cracks and wear in curve track. Gallo [12] studied the relationship between roughness and fatigue
characteristics of 40CrMoV13.9 notched components, with the most evident improvement being
registered for the value of Ra = 0.15 µm.
Metals 2018, 8, 735; doi:10.3390/met8090735
www.mdpi.com/journal/metals

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To estimate the fatigue life, RCF test data of materials should be analyzed by a probabilistic
approach. Yu [13] used the Weibull distribution diagram to analyze the rolling contact fatigue life of
the Fe-Cr coating. Glover [14] studied the Weibull curve of fatigue life conform to the test results by
ball-on-rod tester. The main purpose of this study is to demonstrate the effect of quenching temperature
on microstructure and RCF behavior while using a self-designed rolling contact fatigue testing device.
In this paper, these properties, in addition to damage mechanism and RCF cracks, are discussed.
2. Experimental Procedure
The chemical compositions of 17Cr2Ni2MoVNb steel are presented in Table 1 and they were
prepared by the sequential processes of melting in an electric furnace-ladle refining-vacuum degassing,
then continuous rolling into a
ϕ100 mm round bar. This was followed by quenching at different
temperatures and tempering at 180 ◦C for 2 h, as shown in Table 2.
Table 1. Chemical compositions of 17Cr2Ni2MoVNb steel (wt. %).
C
Si
Mn
Cr
Ni
Al
Cu
Mo
V
Nb
Mg
S
P
0.188 0.015 0.40 1.83 1.63 0.048 0.01 0.31 0.093 0.059 0.007 0.001 0.009
Table 2. Heat treatment of 17Cr2Ni2MoVNb steel.
Samples
Label
Quenching
Temperature
Quenching
Method
Tempering
Temperature
Tempering
Method
◦
◦
1
2
3
900 C × 1 h
oil quenched
oil quenched
oil quenched
180 C × 2 h
water quenched
water quenched
water quenched
◦
◦
1000 C × 1 h
180 C × 2 h
◦
◦
1100 C × 1 h
180 C × 2 h
The platers (8 mm
×
8 mm
×
8 mm) were cut from the heat-treated samples at different
temperatures, which were then polished and corroded with 4% alcohol nitric acid solution. Afterwards,
the microstructure was observed using an optical microscope (OM, LEICA M165C, Barnack, Germany)
and a transmission electron microscope (TEM, FEI Tecnai G20, Hillsboro, OR, USA) operating at
200 kV. An X-ray diffractometer (XRD, Cu Kα radiation, Amsterdam, Holland) was used to identify
the metallographic phase of the materials. Damage surfaces were observed with a scanning electron
microscope (SEM, NOVA NANOSEM 430, Eindhoven, Holland). While the axial surface roughness
of the sample was evaluated using a portable surface roughness tester (Mar Surf, M300C, Esslingen,
Germany).
RCF tests were carried out by using a self-designed rolling contact fatigue testing device,
the schematic of the machine is shown in Figure 1. The lower stationary sample was a disk of
ϕ 48 × 6 mm, the surface roughness and morphology are depicted in Figure 2. The upper rotating
bearing was made of AISI52100 steel with high hardness (60 HRC) [15]. The bearing with 13
uniformity distributed balls were treated as counterpart and balls of bearing with a diameter of
2.79 mm. The surface roughness, Ra, was found to be less than 1.2 µm [16]. The upper rotating
bearing was driven by a DC motor at a speed of 1600 rpm, vertical force was applied by a hydraulic
cylinder, it was measured and recorded on the computer while using a load sensor. The machine of
RCF monitored the fatigue failure by the signals of vibration and torque when the vibration level
exceeded the preset value, the machine would stop automatically. After each test, the bearings and
lubricating oil should be replaced to ensure that the signals acquisition is not being distorted by the
bearing failure or the impurities in the lubricating oil.

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Figure 1. Schematic of the rolling contact fatigue test device. 1-DC motor, 2-Coolant outlet, 3-Coolant
inlet, 4-Spindle, 5-Spindle bearing, 6-Circulating coolant chamber, 7-Bearing, 8-Specimen, 9-Heating
sheet, 10-Rolling bearing, and 11-Hydraulic cylinder.
Figure 2. (a) Surface roughness and (b) morphology.
Each ball was applied 100 N, and contact stress between the bearing and specimen was calculated
by the equation, as follows:
v
u
u


2
1
R1
2
1
+
+
u
1
π
3
R2


t
σ =
6F ×
(1)
2
1−v1
1−v2
E1
E2
where
σ
is the contact stress;
F
is the loading force of a single ball; R1 is the radius of bearing ball,
R2 is the radius of the contact surface with the ball of lower stationary sample, E1 and E2 are the
elastic modulus of bearing and specimen, respectively, ν1 and ν2 are the Poisson’s of bearing and
specimen, respectively.
3. Results and Discussion
3.1. Effect of Quenching Temperature on Microstructure
Figure 3 exhibits the OM micrograph of the 17Cr2Ni2MoVNb quenched at the temperature of
900, 1000, and 1100 ◦C, respectively. It can be concluded from the observations that the quenching
temperature has a great influence on martensite shape. Sun performed on the martensite size was
determined by the martendite start temperature (Ms), the low Ms may lead to obtaining the fine
martensite size [17]. Figure 4 displays the TEM microstructural structures of long and slender ferrite

Metals 2018, 8, 735
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and retained austenite at each quenching temperature. The results reveal that there were much more
dislocations and the austenite size increased with an increasing of the quenching temperature.
(a)
(b)
20 μm
20 μm
(c)
50 μm
Figure 3. Optical microscopy (OM◦) micrographs of 17Cr2Ni2MoVNb steel quenched at different
◦
◦
temperatures of (a) 900 C, (b) 1000 C, and (c) 1100 C.
(a)
(b)
260 nm
FB
140 nm
FB
RA
Dislocations
FB
RA
Dislocations
(c)
350 nm
Dislocations
RA
Figure 4. Transmission electron microscopy (TEM) micrographs of 17Cr2Ni2MoVNb steel quenched at
◦
◦
◦
different temperatures of (a) 900 C, (b) 1000 C, and (c) 1100 C.

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Figure 5 shows the X-ray diffraction (XRD) patterns. It has been reported in our previous study
that the results of XRD patterns were similar and they indicate the test conditions were stable and the
samples preparation was qualified [18]. It is well known that the effective methods to improve the
strength in steel mainly include fine grain strengthening and precipitation strengthening [19]. Using
the XRD method, the average grain size and dislocation density can be quantified. The grain size is
investigated by the Scherrer equation, as follows:
Kλ
β cos θ
D =
(2)
where
D
is the mean size of crystal,
K
is the dimensionless shape factor, and
λ
is the X-ray wavelength,
β is the breadth at half the maximum peak intensity, and θ is the Bragg angle (in degrees).
Figure 5. X-ray diffractometer (XRD) patterns of 17Cr2Ni2MoVNb steel quenched at different
temperatures.
Figure 6a indicates that a linear relationship with 0.002 slope existed between the mean gain
size and the quenching temperature from 900 to 1100 ◦C. It also should be noted that the higher the
◦
quenching temperature, the larger the grain size. At quenching temperatures of 900, 1000, and 1100 C,
the mean grain sizes were approximately 19.63, 19.75, and 19.98 nm, respectively.
Using the XRD method, the dislocation density can be calculated from the XRD pattern by the
following equation:
e2
b2
ρ = 14.4
(3)
is Bragg’ s vector of dislocation in α − Fe
where
ρ
is the dislocation density,
e
is the microstrain, and
b
.
(a)
Figure 6.
(a) the mean size of crystal and (b) dislocation density of samples at different quenching
temperatures.

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Figure 6b shows that the dislocation density increased evidently with increasing of the quenching
◦
◦
◦
◦
temperature from 900 C to 1000 C, and decreased from 1000 C to 1100 C. This was consistent with
previous report on the effect of quenching temperature on dislocation density of bainitic steel [20].
The dislocation density of 22.97
of 900, 1000, and 1100 ◦C, respectively.
×
1013, 26.48
×
1013, and 22.23
×
1013 m-2 at quenching temperatures
3.2. Weibull Distribution
The Weibull distribution is widely used to assess the statistical behavior of the fatigue
life [21 22]. In this work, two-parameter weibull distribution is used to characterize the RCF life
of 17Cr2Ni2MoVNb steel. The cumulative distribution function is given as:
,
ꢀ
ꢁ
β
N
Na
F(N) = 1 − exp[−
]
(4)
where F(N) is the probability of fatigue failure;
N
is the RCF life;
β
is the shape parameter of fatigue
life; and, Na is the characterizes parameter of life.
Figure 7 shows the weibull curves of life and Table 3 shows the detail result of the fatigue life.
The specified life, median life, and characteristic life of the specimen of quenched at 1000 ◦C were
2.11 × 106, 2.28
×
106, and 2.31
×
106 under the contact st◦ress of 3.2 GPa, respectively, which were
◦
larger than that of the samples quenched at 900 C and 1100 C. The mean life of the samples quenched
at 1000 ◦C was 1.46 times and 1.89 times that of quenched at 900 ◦C and 1100 ◦C, respectively. It is
clear that the slope of the Weibull curve of quenched at 1000 ◦C is obviously higher than that of the
other two specimens, which that indicates the distribution of the specimen data and the failure time
are stable. It can be observed that the dislocation density of the samples quenched at 1000 ◦C was
more significant when compared to that of other samples, the improved dislocation density of the
samples may be attributed to the fatigue life. The specified life, median life, characteristic life, and the
Weibull slope are summarized in Table 4.
Figure 7. Weibull curves of fatigue life of 17Cr2Ni2MoVNb steel quenched at different temperatures.

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Table 3. Detail result of test date steel.
h
i
−1
◦
◦
◦
1100 C
Samples Label
900
C
1000
C
F(Ni)
lg lg 1 − F(Ni)
1
2
3
4
5
6
7
8
9
103,400
137,800
209,300
274,300
477,000
487,500
536,900
543,400
1,742,000
245,100
367,300
572,000
637,500
707,200
731,900
949,000
1,056,800
1,331,200
98,600
107,600
209,800
237,800
289,300
497,000
566,200
655,600
832,600
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
−1.34
−1.014
−0.81
−0.654
−0.521
−0.4
−0.282
−0.156
0
Table 4. Typical values of the rolling contact fatigue (RCF) life.
Quenching
Temperature
Mean
Life/105
Specified
Life/105
Median
Life/105
Characteristic
Life/105
Weibull
Plot Slope
◦
900 C
5.01
7.33
3.88
1.96
2.11
1.90
2.26
2.28
2.16
2.32
2.31
2.21
1.10115
1.85714
1.24786
◦
1000 C
◦
1100 C
3.3. Surface Fatigue Damage
Figure 8 exhibits the micrographs of the damage after RCT tests. In order to compare failure
mechanism at different quenching temperatures, three groups of tests with similar fatigue life were
selected for observation. Figure 8a shows the worn surface morphology of the sample quenched at
900 ◦C with a fatigue life of 543,400 cycles. Delamination was the main damage mode of the sample
◦
quenched at 900 C, and some spallings propagated to cracks under the influence of cyclic stress.
With the increased of testing time, the local plastic strain accumulated gradually. It should be noted
that the ball, contact surface of sample, and lubricating oil form a high-pressure oil chamber under the
action of high-speed rotation. Those high pressure oils were squeezed into cracks and caused a great
impact on the interior of the cracks.
◦
Figure 8b shows the worn surface morphology of the sample quenching at 1000 C with a fatigue
life of 572,000 cycles. A large number of fatigue pits on the contact surface, marked as arrows, some of
pits have gradually expanded to the larger ones on the surface of quenched at 1000 ◦C. It is believed
that the fatigue pits can affect the roughness of the contact surface, which intensified the wear of the
surface. Fatigue pits further expanded into cracks to impact on fatigue life of the specimens under
stress concentration. Similar results have been reported by Fang, who concluded that micro-cracks
preferentially initiate at the concave where the rough surface causes stress concentration [23].
Figure 8c shows the worn surface morphology of the sample quenched at 1100 ◦C w◦ith a fatigue
life of 566,200 cycles. It indicates that the surface damage mechanism of quenched at 1100 C is similar
to that at 900 ◦C. However, there some sub-cracks on the subsurface in Figure 8c, and the sub-cracks
propagated to the peeling and delamination. While, the debris agglomerated in the contact surface as
a moving particle plowing the surface to generate the abrasive pits.
Figure 8d–f show the energy dispersive X-ray analysis (EDS) patterns of delamination and peeling.
It is observed from Figure 8d,f that the S and Cl were found in the delamination, indicating that a bond
was formed between the lubricant and the delamination under the influence of the cyclic impact of
high pressure oil. However, the S and Cl were not found in the pitting in Figure 8f, indicating that the
lubricating oil has good fluidity in this area.

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d
e
f
(f)
Figure 8. Typical micrographs of the damage: (
a
) Quenched at 900 ◦C contact stress3.2 GPa and
◦
543,400 cycles to failure; (
b
) Quenched at 1000 C contact stress 3.2 GPa and 572,000 cycles to failure;
◦
(c
) Quenched at 1100 C contact stress 3.2 GPa and 566,000 cycles to failure and EDS graphs at different
◦
◦
◦
temperatures of (d) 900 C, (e) 1000 C, and (f) 1100 C.
3.4. Subsurface Fatigue Damage
Figure 9 shows the cross-sectional subsurface damage of the samples at different quenching
temperatures. It is obvious in Figure 9a that the cracks propagate parallel to the surface and the
different propagation angles of cracks are growing to lamellar structure cracks. In addition, the surface
and surface cracks join with each other meanwhile subsurface cracks develop to the surface of the

Metals 2018, 8, 735
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sample quenched at 900 ◦C, and the depth of plastic deformation layer in the depth direction is about
◦
◦
22
µ
m. Figure 9b shows the SEM micrographs of the cracks of the sample quenching at 1100 C.
◦
How cracks propagate on the sample quenched at 1000 C is similar to the sample quenched at 900 C
under the contact stress of 3.2 GPa, The depth of plastic deformation layer in the depth direction is
about 34 µm. Figure 9c exhibits the morphology of peeling on cross-sectional subsurface. It can be
found that the subsurface cracks and lamellar structure cracks join with each other and the depth of
plastic deformation layer is about 40 µm.
Figure 9. Micrographs of subsurface damage: (
a
) Quenched at 900 ◦C contact stress 3.2 GPa and
◦
543,400 cycles to failure; (
b
) Quenched at 1000 C contact stress 3.2 GPa and 572,000 cycles to failure;
◦
and, (c) Quenched at 1100 C contact stress 3.2 GPa and 566,000 cycles to failure.

Metals 2018, 8, 735
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Moreover, the propagation angles of the sample at different quenching temperatures were about
8.6◦, 5.4◦, and 3.1◦, respectively, it should be noted that there was a tread of convergence between
surface and subsurface cracks, small extension angles were prone to peeling. This was consistent with
Ma [24], who reported the wear and damage characteristics of rail material.
It is clear that the quenching temperatures make a difference in damage mechanism of RCF cracks.
Some cracks propagate along with an increasing of the quenching temperature, while cracks grow
upward to the surface, and the delamination emerges under the influence of cyclic stress (Figure 8a,c).
Moreover, the subsurface reveals serious lamellar structure cracks at 1100 ◦C (Figure ◦10a), and some
cracks initiate on the surface and form the peeling (Figure 10c). Quenched at 1000 C, dislocation
density enhances the resistance to damage, as a result, the cracks get hard to propagate. Therefore,
the lamellar structure cracks in the depth direction are the least (Figure 10b).
(b)
(a)
Lamellar structure cracks
Lamellar structure cracks
(c)
Cracks propagate to peeling
Figure 10. Schematic of fatigue damages: (◦
a
) Quenched at 900 ◦C contact stress 3.2 GPa and
543,400 cycles to failure; (b) Quenched at 1000 C contact stress 3.2 GPa and 572,000 cycles to failure;
◦
and, (c) Quenched at 1100 C contact stress 3.2 GPa and 566,000 cycles to failure.
4. Conclusions
In this work, the effect of quenching temperatures on microstructure and rolling contact fatigue
behaviors of 17Cr2Ni2MoVNb steel are evaluated. In order to address this challenge, a set of tests were
conducted on 17Cr2Ni2MoVNb. Based on the results, the main conclusions can be drawn, as follows:
(1). Using the XRD method, the average grain size increased while quenching temperature
increased. The dislocation density increased first and then reduced.
◦
(2). Under the contact stress of 3.2 GPa, samples at the quenching temperature of 1000 C had the
highest RCF life, the average life was 7.33
and 1100 ◦C, respectively.
×
106, which was 1.46 times and 1.89 times that of 900 ◦C
(3). The failure mechanism ◦of the samples quenched at 1000 ◦C was pitting, and delamination
◦
was the main failure mode of 900 C and 1100 C. The effect of lubricating oil on the pitting was mainly
lubrication, and the effect on delamination was impact damage.
(4). The thicknesses of the plastic deformation layer were 22
µm, 34 µm, and 40 µm with the
quenching temperatures of 900, 1000, and 1100 ◦C, respectively. While cracks grew upward to the

Metals 2018, 8, 735
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surface and joined with each other to form lamellar structure cracks. However, the peeling was easy to
emerge when the samples quenched at 1100 ◦C.
Author Contributions: Both authors contributed equally to the work.
Funding: This research received no external funding.
Acknowledgments: The authors would like to thank the National Engineering Research Center of Near-Net-Shape
Forming for Metallic Materials, State Key Laboratory of Smart Manufacturing for Special Vehicle as well as
Transmission System and State Key Laboratory of Internal Combustion Engine Reliability for material preparation
and mechanical properties testing.
Conflicts of Interest: The authors declare no conflict of interest.
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