Page 140 - 《摩擦学学报》2021年第6期

第 6 期 马彦军, 等: Ag 2 S纳米粒子原位合成以增强PAI涂层机械和摩擦学性能 925

the composite coating. The average particle size of Ag 2 S nanoparticles increased as the single-source precursor content
increased in the coating. Specifically, when the content of Ag 2 S nanoparticles was 1.0%, the particle size of Ag 2 S
nanoparticles was 24 nm, and the size distribution was relatively uniform. When the weight fraction of Ag 2 S
nanoparticles increased to 3.0%, 5.0%, 7.0% and 9.0%, Ag 2 S nanoparticles showed a bimodal size distribution. The
particle size of Ag 2 S nanoparticles was 35 nm and 10 nm when the weight fraction was 3.0%, 75 nm and 12 nm when
the content was 5.0%, 116 nm and 19 nm when the weight fraction was 7.0%, 230 nm and 26 nm when the weight
fraction was 9.0%. These results showed that the amount of single-source precursor added in the coating greatly affected
the particle size of Ag 2 S nanoparticles synthesized in-situ, that is, the particle size and size distribution of Ag 2 S
nanoparticles can be effectively controlled by adjusting the added content of the single-source precursor.
Subsequently, the mechanical properties (micro-hardness, elastic modulus, plastic deformation ability and scratch
resistance performance) of the PAI composite coatings reinforced by in-situ synthesized Ag 2 S nanoparticles with
different contents were studied. The results demonstrated that the micro-hardness and elastic modulus of the composite
coating were significantly improved after Ag 2 S nanoparticles were in-situ introduced. As the content of Ag 2 S
nanoparticles increased, the micro-hardness and elastic modulus of the nanocomposite coatings both showed a trend of
increasing first and then decreasing. In particular, when the weight fraction of Ag 2 S nanoparticles was 5.0%, the
nanocomposite coating exhibited the largest micro-hardness (H=372 MPa) and elastic modulus (E=6 497 MPa), which
increased by 39.85% and 95.63% compared with those of the pure PAI coating without Ag 2 S nanoparticles (H=
266 MPa, E=3 321 MPa), respectively. Besides, the addition of in-situ synthesized Ag 2 S nanoparticles significantly
reduced the critical displacement (corresponds to indentation depth) and residual depth of the coating. The maximum
displacement of the pure PAI coating was 1 600.35 nm, and the residual depth was 780.16 nm, which were much higher
than those of other coatings containing in-situ synthesized Ag 2 S nanoparticles. When the Ag 2 S nanoparticle content was
5.0%, the critical displacement and residual depth of the coating decreased most obviously, the maximum displacement
dropped to 1 192.20 nm, and the residual depth dropped to 575.44 nm. In other words, the in-situ synthesized Ag 2 S
nanoparticles greatly affected the plastic deformation resistance and elastic recovery ability of the composite coating,
and the enhancement effect was most remarkable when the weight fraction was 5.0%.
The scratch resistance test results of the nanocomposite coating showed that the critical load where coating damaged
to begin of the pure PAI coating without Ag 2 S nanoparticles was lower, of 7.76±0.12 N. After Ag 2 S nanoparticles were
introduced in-situ, the critical load for nanocomposite coating increased. The critical load for nanocomposite coatings
with Ag 2 S nanoparticles weight fraction of 1.0%, 3.0%, 5.0%, 7.0%, 9.0% increased to 9.63±0.06 N, 10.16±0.04 N,
12.64±0.27 N, 11.60±0.05 N and 8.26±0.21 N, respectively. Obviously, when the content of Ag 2 S nanoparticles was
5.0%, the critical load of the nanocomposite coating was the largest, which meant that various amount of Ag 2 S
nanoparticles displayed different enhancement effects on the bonding strength and internal strength of the coating, and
the optimal weight fraction of Ag 2 S nanoparticles was 5.0%. It can be seen from these results that the in-situ synthesized
Ag 2 S nanoparticles can effectively enhance the mechanical properties of the nanocomposite coating, and the
enhancement effect had a large dependence on their content and size. When the weight fraction was 5.0%, the Ag 2 S
nanoparticles with a balanced size and bimodal distribution showed better enhancement effect.
The analysis and evaluation of the dynamic thermomechanical properties of the nanocomposite coating showed that
the introduction of the in-situ synthesized Ag 2 S nanoparticle improved the storage modulus (reflecting the stiffness of
the material) in the glassy region of the coating. The storage modulus value of pure PAI coating was lowest (2 424 MPa).
As the weight fraction of Ag 2 S nanoparticles increased from 1.0% to 9.0%, the storage modulus of the nanocomposite
coating increased first and then decreased. When their weight fraction was 5.0%, it showed the highest storage modulus
of 3 553 MPa, which was increased by 46.6% compared with that of the pure PAI coating, corresponding to providing a
higher carrying capacity. In addition, the glass transition temperature of the pure PAI coating was 153 ℃, and the glass
transition temperature of the nanocomposite coating reinforced with Ag 2 S nanoparticles synthesized in-situ was greatly
increased. Especially for the 5.0% Ag 2 S nanoparticle reinforced nanocomposite coating, the glass transition temperature
increased to 175 ℃, which was higher than that of other coatings. In addition, the introduction of in-situ synthesized
Ag 2 S nanoparticles made the peak intensity of the loss factor-temperature curve of the enhanced nanocomposite coating
lower than that of the pure PAI coating, and the loss factor value of the 5.0% Ag 2 S nanoparticle enhanced
nanocomposite coating was the lowest, which showed the stronger energy dissipation capability. All these results
demonstrated that the in-situ synthesized Ag 2 S nanoparticles greatly affected the dynamic thermomechanical properties