# Exploring Surface-Driven Mechanisms for Low-Temperature Sintering of Nanoscale Copper
## 3 Results and Discussion
### Mechanical Properties of Sintered Samples
#### 3.2.2 Young's Modulus and Tensile Strength
(**b**) The Young’s modulus measured from the slope of the stress–strain curve in the strain phase of less than 1%. the plastic deformation stage without exhibiting a significant sudden fracture. As the stretching process continues, the neck region becomes increasingly thinner and longer until it ultimately fractures due to excessive thinning. At 600 K, the porosity of the sample has largely closed, and no distinct granular appearance can be observed. As mentioned earlier, at 600 K, due to the rapid surface dynamics of the nanoparticles, numerous atoms are undergoing rapid dynamic motion on the inner surfaces of the pores within the sintering system. These atoms facilitate the rapid closure of the pores and promote structural adjustments and reconstruction within the sintering system, resulting in a significant improvement in the morphology of the sintered sample compared to that at 300 K. However, the strain cloud diagram indicates that since small pores still exist within the sintering system, material failure will initiate from these pores during the stretching process. Consequently, the sample sintered at 600 K enters the plastic deformation stage at a strain of 5% without experiencing brittle fracture. Its tensile strength shows a significant increase compared to samples sintered at 300 K, 400 K, and 500 K, approximately 1.5 to 3 times higher. For the sample sintered at 900 K, the porosity has completely closed. Only a small number of dislocations and slip planes remain that have not had time to adjust. At this point, the sintered sample exhibits extremely high tensile strength, maintaining an elastic state until a strain of 9% is reached, at which point it undergoes brittle fracture, leading to a substantial reduction in strength and entering the plastic deformation stage. In fact, samples at temperatures of 700 K, 800 K, 900 K, and 1000 K have all demonstrated characteristics of brittle materials, contrasting with the weak ductility observed in samples below 600 K. For pure copper materials, they are classified as brittle rather than ductile, and the results obtained here are fundamentally similar to those found in experiments. As shown in Figure 9b, the tensile strength at 700 K has significantly increased--nearly 2 to 3 times that of the tensile strength at 300 K to 500 K. The characteristic changes in the material  
Figure 10: The atomic shear strain during the stretching processes at 300 K, 600 K, and 900 K is presented. The corresponding simulation steps are indicated beneath each strain cloud diagram. The red arrows in the figure highlight the initial locations of structural failure. during uniaxial tensile testing occur between the sintering temperatures of 600 K and 700 K, marking the transition from brittle material characteristics to those of weak ductility. This transformation in material properties is closely linked to the rapid surface dynamic state that emerges at 600 K. Before the temperature reaches 600 K, the material is filled with pores and defects, which quickly lead to failure and subsequent plastic deformation when subjected to unidirectional tensile forces. Once the rapid surface dynamic state appears, the pores within the material begin to close, forming a system with higher strength. The emergence of this dynamic state significantly enhances the mechanical strength of the sintered nanomaterials, allowing them to achieve tensile strengths comparable to those of samples sintered at temperatures close to their melting points, even at lower temperatures.