•A series of TiN/Ni nanocomposite films with different Ni content were synthesized.•The TiN/Ni film is consisted of TiN nanocrystallites surrounded by Ni interface.•Ni interface can grow coherently with TiN nanocrystallites with the low Ni content.•The strengthening of TiN/Ni film can be explained by coherent-interface mechanism.A series of TiN/Ni nanocomposite films with different Ni content were synthesized by reactive magnetron sputtering. The microstructural evolution, mechanical properties and strengthening mechanism of TiN/Ni nanocomposite film were studied. When Ni:Ti ratio is less than 1:24, the small amount of Ni can be dissolved in the TiN matrix, leading to the slight decrease of the hardness and elastic modulus. When Ni:Ti ratio rises to 4:21, Ni inclines to separate from TiN due to the thermodynamic incompatibility as an interfacial phase and grow coherently with adjacent TiN crystallites. As a result, the TiN/Ni film was remarkably strengthened with the maximal hardness and elastic modulus of 33.3 GPa and 373 GPa. As Ni:Ti ratio further increases to 5:20, Ni interface transforms into amorphous state, leading to the destruction of the epitaxial growth structure and the rapid decrease of hardness and elastic modulus. The strengthening effect of TiN/Ni nanocomposite film can be attributed to the coherent interface between Ni interfacial layers and TiN crystallites.

•A series of NbSiN nanocomposite films with different Si content were synthesized.•The NbSiN film is consisted of NbN nanocrystallites surrounded by Si3N4 interface.•Si3N4 interface can grow coherently with NbN crystallites with the low Si content.•The structural model of NbSiN nanocomposite film can be expressed by nc-MeN/c-Si3N4.•The strengthening of NbSiN film can be explained by coherent-interface mechanism.Currently, the strengthening mechanism and microstructural model of nanocomposite films are controversial. The aim of the present study is to elucidate the microstructure and strengthening mechanism of the NbSiN nanocomposite film. A series of NbSiN films with different Si contents are synthesized by reactive magnetron sputtering, and the films are characterized as nanocomposite structures with NbN nanocrystallites surrounded by the Si3N4 interfacial phase. When the Si:Nb ratio is < 1:4, the Si3N4 interface can be crystallized, and it prefers to grow coherently with the adjacent NbN crystallites, leading to the strengthening effect of the film. The maximum values for the hardness and elastic modulus of the NbSiN nanocomposite film reach 34.2 GPa and 287 GPa, respectively. Using the high-resolution transmission electron microscopy (HRTEM) observations, we verified that the Si3N4 interfaces can be found in a crystallized state when the NbSiN nanocomposite film is strengthened, and can coordinate the misorientations between the adjacent NbN nanocrystallites and preserve the coherently-epitaxial growth with these nanocrystallites. The strengthening effect of the NbSiN nanocomposite film can be explained by the coherent-interface mechanism.

•The CrAlN/SiO2 nanomultilayered films were prepared by reactive magnetron sputtering.•Effects of SiO2 layer thickness on structure and mechanical properties were studied.•The amorphous SiO2 could be crystallized and grow epitaxially with CrAlN layers.•The film shows an evident superhardness effect with maximal hardness of 38.9 GPa.•The hardening can be explained by modulus-difference and alternating-stress theories.The CrAlN/SiO2 nanomultilayered films with different SiO2 layers thickness were synthesized by reactive magnetron sputtering. The effects of SiO2 layer thickness on the microstructure and mechanical properties of CrAlN/SiO2 nanomultilayered films were studied. The results reveal that, when SiO2 layer thickness is less than 0.7 nm, originally amorphous SiO2 layers can be forced to crystallize under the “template effect” of NaCl-structured CrAlN layers and grow epitaxially with them, resulting in the preservation of columnar growth structure and remarkable superhardness effect with the maximum value of hardness of 38.9 GPa. As the SiO2 layer thickness exceeds 0.7 nm, however, SiO2 layers transform back into amorphous state, which destructs the epitaxial structure between CrAlN and SiO2 layers, leading to disappearance of columnar growth character and decrease of mechanical properties. The superhardness effect of CrAlN/SiO2 nanomultilayered film can be attributed to the joint effects of modulus-difference and alternating-stress strengthening mechanisms.

•TiSiN films inserted with CrAlN nanolayers of different thicknesses were synthesized.•The nanocomposite structure of TiSiN was damaged with the insertion of CrAlN nanolayers.•The film can be hardened after initial softening with the increase of CrAlN thickness.A series of TiSiN films inserted by CrAlN nanomultilayers with different thicknesses was prepared by reactive magnetron sputtering. The influences of CrAlN layer thickness on the microstructure and hardness of films were investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and nano-indentation techniques. The insertion of CrAlN nanomultilayers destructs the nanocomposite structure of TiSiN film, leading to the decrease of hardness. As the CrAlN layer thickness increases to 2.5 nm, CrAlN layers are inclined to grow epitaxially with TiSiN layers in order to lower the interfacial energy. As a result, the TiSiN film can be further strengthened with the maximal hardness of 53.9 GPa. As the CrAlN layer thickness further increases to 3.0 nm, the epitaxial growth structure between TiSiN and CrAlN layers is broken, resulting in the deterioration of hardness.

•The HfC/SiC nanomultilayered films were prepared by reactive magnetron sputtering.•Effects of SiC layer thickness on structure and mechanical properties were studied.•The amorphous SiC layers could be crystallized and grow epitaxially with HfC layers.•The maximum hardness and elastic modulus reached 36.2 and 419 GPa, respectively.A series of HfC/SiC nanomultilayered films with different SiC layer thickness were synthesized by reactive magnetron sputtering. The effect of SiC layer thickness on the microstructure and mechanical properties of HfC/SiC nanomultilayered films were studied. When SiC layer thickness was less than 0.9 nm, originally amorphous SiC layers were forced to crystallize and grow epitaxially with HfC layers, resulting in the improvement of crystallization integrality and enhancement in hardness and elastic modulus. The maximum hardness and elastic modulus could reach 36.2 GPa and 419 GPa, respectively. With further increase of SiC layer thickness, SiC layers changed back to amorphous state and damaged the epitaxial growth structure, leading to deterioration of mechanical properties.

TiN nanolayers with different thicknesses were inserted in TiSiN nanocomposite film by magnetron-sputtering technique. The influences of TiN insertion nanolayers with different thicknesses on microstructure and mechanical properties of TiSiN film were investigated X-ray diffraction, high-resolution transmission electron microscopy, scanning electron microscopy, and nanoindentation techniques. When the TiN insertion layer thickness is <0.5 nm, TiN nanolayers can coordinate the misorientations between TiN nanocrystallites in adjacent TiSiN layers, leading to the transformation from the nanocomposite structure with TiN nanocrystallites encapsulated by SiNx interfacial phase into columnar crystal structure, and disappearance of the strengthening effect from the nanocomposite structure. When the TiN insertion layer thickness increases to 1.0 nm, the film is strengthened with the epitaxial growth structures between TiSiN and TiN layers. As the TiN insertion layers further thicken, the hardness and elastic modulus evidently decrease, which can be attributed to the breakage of epitaxial growth structures between TiSiN and TiN layers.

CrAlN/SiNx nanomultilayers with different SiNx layer thicknesses were synthesized by reactive magnetron sputtering. The microstructure and mechanical properties were investigated by X-ray diffraction, high-resolution transmission electron microscopy and nano-indentation techniques. The average crystallite size, microstrain and average dislocation density of CrAlN/SiNx nanomultilayers with different SiNx layer thicknesses were evaluated by X-ray diffraction line profile analysis method. The results indicated that, when SiNx layer thickness was below 0.6 nm, SiNx was forced to crystallize and grew epitaxially with CrAlN layers, resulting in the decrease of average dislocation density and the enhancement in hardness and elastic modulus. As the SiNx layer thickness further increases, the epitaxial growth was firstly interrupted and then crystallized SiNx layers transformed back to amorphous state, leading to the increase of average dislocation density and the decrease of hardness and elastic modulus. An energy balance model was established to explain the microstructure evolution.Highlights► Superhardness effect was found in reactively synthesized CrAlN/SiNx nanomultilayers. ► The maximum hardness and elastic modulus respectively reach 37.6 GPa and 437 GPa. ► Microstructural evolution was studied during disappearance of superhardness effect. ► An energy balance model was established to explain the microstructure evolution.

A series of CrAlN/SiC nanomultilayers with different SiC layer thickness were synthesized by reactive magnetron sputtering. The microstructure and mechanical properties were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM) and nano-indentation techniques. The results indicated that, when SiC layer thickness was less than 0.8 nm, amorphous SiC layers were forced to crystallize under the template effect of CrAlN layers and grew epitaxially with CrAlN layers, resulting in abnormal enhancement of mechanical properties. The maximum hardness and elastic modulus could respectively reach 35.4 GPa and 431 GPa when SiC layer thickness was 0.8 nm. With further increase of SiC layer thickness, SiC layers changed back to amorphous state and broken coherent growth structure of nanomultilayers, leading to the decrease of hardness and elastic modulus.Highlights► The novel CrAlN/SiC nanomultilayers were produced by reactive magnetron sputtering. ► The amorphous SiC layers were crystallized and grew epitaxially with CrAlN layers. ► The maximum hardness and elastic modulus respectively reach 35.4 GPa and 431 GPa.

The novel TiAlN/AlON nanomultilayers with different AlON layer thickness were synthesized by reactive magnetron sputtering. The microstructure and mechanical properties were investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM) and nano-indentation techniques. The results indicated that, under the template effect of fcc (face-centered cubic) TiAlN layers, originally amorphous AlON layers were crystallized and grew epitaxially with TiAlN layers when AlON layer thickness was below 0.7 nm. Accordingly, the hardness and elastic modulus of the nanomultilayers increase and reach the maximum values of 36.2 and 385.6 GPa, respectively. With further increase of AlON layer thickness, AlON layers transformed back into amorphous state and broken the coherent growth of nanomultilayers, leading to the decrease of hardness and elastic modulus. The strengthening mechanism of TiAlN/AlON nanomultilayers was further discussed.Highlights► The novel TiAlN/AlON nanomultilayers were produced by reactive magnetron sputtering. ► The amorphous AlON layers were crystallized and grow epitaxially with TiAlN layers. ► The maximum hardness and elastic modulus, respectively, reach 36.2 GPa and 385.6 GPa.

A nanocrystalline surface layer is synthesized in Ni by surface mechanical attrition treatment (SMAT). The characterization of microstructure and composition indicates that foreign elements from hardened balls can permeate and diffuse into the surface layer during SMAT, which can further diffuse and homogenize in the surface layer when annealing at high temperature, leading to formation of new alloy. Foreign elements permeating into the surface layer during SMAT followed by diffusing and homogenizing at high temperature provide an alternative effective technology for surface modification.Research highlights▶ The primary aim of this manuscript is to investigate the effect of annealing process on the diffusion of foreign elements permeated into the nanocrystalline Ni surface layer and its influence on the composition and structure of surface layer. ▶ The results indicate that foreign elements from the hardened balls can be pressed and diffused into the surface layer during SMAT, resulting in the concentrated distribution in the treated surface. In the course of subsequent annealing, foreign elements can further diffuse and homogenize in the surface layer, leading to the formation of new kind of alloy in the surface layer. ▶ Foreign elements permeate into the surface layer during SMAT, further diffuse and homogenize when annealing at high temperature, and finally form the new compound, which can provide an alternative effective technology for surface modification.

TiAlN/SiO2 nanomultilayers with different SiO2 layer thickness were synthesized by reactive magnetron sputtering. The microstructure and mechanical properties were investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and nano-indentation. The results indicated that, under the template effect of B1-NaCl structural TiAlN layers, amorphous SiO2 was forced to crystallize and grew epitaxially with TiAlN layers when SiO2 layer thickness was below 0.6 nm, resulting in the enhancement of hardness and elastic modulus. The maximum hardness and elastic modulus could respectively reach 37 GPa and 393 GPa when SiO2 layer thickness was 0.6 nm. As SiO2 layer thickness further increased, SiO2 transformed back into amorphous state and broken the coherent growth of nanomultilayers, leading to the decrease of hardness and elastic modulus.