氮化铝（AlN）陶瓷常见的坯体成型与烧结方法概述

A brief introduction to the molding and sintering methods of common aluminum nitride (AlN) ceramics

氮化铝（AlN）是一种六方纤锌矿结构的共价键化合物，晶体结构和微观组织如图1所示。室温强度高、热膨胀系数小、抗熔融金属侵蚀的能力强、介电性能良好，这些得天独厚的优点使其成为高导热材料而引起国内外的普遍关注。作为高性能的介电陶瓷，氮化铝可以取代碳化硅，甚至部分取代氧化铝，被视为新一代很有发展前途的优良的基片材料。

AlN is a covalent bond compound with hexagonal wurtzite structure. The crystal structure and microstructure are shown in Fig. 1. High strength at room temperature, low coefficient of thermal expansion, strong resistance to molten metal corrosion, good dielectric properties, these unique advantages make it become a high thermal conductivity materials and arouse widespread concern at home and abroad. As a high-performance dielectric ceramics, aluminum nitride can replace silicon carbide, or even partly replace alumina, which is regarded as a new generation of promising substrate materials.

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常见的AlN坯体成型方法

Common method for forming AlN billet

由氮化铝粉末制备氮化铝陶瓷坯体，需要利用成型工艺把粉体制备成坯体，然后再进行烧结工作。氮化铝成型工艺主要有干压成型、等静压成型、流延法成型和注射成型等。

The preparation of aluminium nitride ceramic green body from aluminium nitride powder requires the use of molding technology to prepare the powder green body, and then sintering. The forming process of AIN is mainly dry pressing, isostatic pressing, tape casting and injection molding.

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One

干压成型

Dry pressing

图2为干压成型机。干压成型（轴向压制成型）是将经表面活性剂改性等预处理的 AlN 粉体加入至金属模具中，缓慢施加压力使其成为致密的坯体成型工艺。实质是借助外部施压，依靠AlN粉末颗粒之间的相互作用力使坯体保持一定的形状和致密度高致密坯体，其有利于陶瓷烧结，可以降低烧结温度，提高陶瓷致密度。由于AlN粉末易水解，干压成型中常用的水-聚乙烯醇（PVA）不能用于AlN粉末的压制，可选用石蜡与有机溶剂代替。

Fig. 2 is a dry press molding machine. Dry compression molding (axial compression molding) is a process in which the pre-treated AlN powder modified by surfactant is added to the metal mold, and the pressure is applied slowly to make it a compact green body forming process. Essentially, by means of external pressure and the interaction force between the AlN powder particles, the green body keeps a certain shape and high density, which is beneficial to the sintering of ceramics, can reduce the sintering temperature and increase the density of ceramics. Because of the easy hydrolysis of AlN powder, water-polyvinyl alcohol (PVA), which is commonly used in dry compaction, can not be used in the compaction of AlN powder, and paraffin and organic solvents can be used instead.

优点：

Advantage:

干压成型法操作简单，工艺环节少，效率高。

The dry pressing method is simple in operation, less in technological process and high in efficiency.

缺点：

Shortcomings:

不能压制复杂几何形状的坯体；需严格控制压力大小，过大或过小均不利于得到高致密度AlN陶瓷烧结件。

Complicated shape of green body can not be pressed; the pressure should be strictly controlled, too large or too small are not conducive to high density AlN ceramic sintered parts.

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图2 干压成型机

Fig. 2 dry pressing machine

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Two

等静压成型

Isostatic pressing

等静压成型是传统干压法的改进方法，将AlN 粉体置于高压容器中，利用液体的不可压缩性和液体对压力传导的特性，将粉体置于弹性材料制造的成型模具中，从不同的方向对待压粉体进行均匀施压，以液体对模具进行加压而使坯体成型的方法。

Isostatic pressing is an improved method of traditional dry pressing. AlN powder is placed in a high pressure vessel, and the powder is placed in a mold made of elastic material according to the incompressibility of the liquid and the conductivity of the liquid to the pressure. Method for forming green body.

优点：

Advantage:

坯体的致密度较高，密度分布均一，可以近净尺寸成型。

The density of the green body is high and the density distribution is uniform. It can be formed near net size.

缺点：

Shortcomings:

成型设备昂贵，且存在脱模问题，限制了将其应用于大规模的工业生产。

The molding equipment is expensive and there is a problem of demoulding, which limits its application to large-scale industrial production.

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Three

流延成型

Casting

流延成型法是一种十分重要的陶瓷基片的成型工艺。将AlN 粉体与复合粘合剂（分散剂、溶剂、粘结剂和增塑剂组成）混合均匀后得到 AlN 流延料浆，除气等过程处理后的浆料倒入料斗，经刮刀口后，形成厚度均匀、表面光滑附着于光滑带上的薄层，再经干燥后制备成具有良好韧性的坯体；排胶烧结之后得到 AlN 基片材料。

Tape casting is a very important technology for forming ceramic substrates. AlN tape slurry is obtained by mixing AlN powder with composite binder (composed of dispersant, solvent, binder and plasticizer). After degassing and other processes, the slurry is poured into hopper. After scraper opening, a thin layer with uniform thickness and smooth surface is formed which adheres to the smooth belt. After drying, the slurry has good toughness. The AlN material is obtained after sintering.

优点：

Advantage:

设备简单，可以连续操作，生产率高，自动化程度高等。

The equipment is simple and can be operated continuously, with high productivity and high automation.

缺点：

Shortcomings:

要求较为严格，料浆就工艺参数的变化十分敏感，成型坯体表面粗糙且结合不充分，强度较低，干燥过程中易出现起泡开裂、弯曲变形等现象；同时流延成型只能用于片状材料的生产。

The slurry is very sensitive to the change of technological parameters, the surface of the green body is rough and insufficient, the strength is low, the drying process is prone to foaming cracking, bending deformation and other phenomena; at the same time, tape casting can only be used in the production of sheet materials.

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注射成型

injection molding

AlN陶瓷注射成形是粉末注射成形应用于陶瓷粉末成型的一种方法，以塑料注射成形工艺为基础，经过技术改进而产生的成型技术。其基本过程为先在AlN粉末中加入粘结剂并使其混合均匀，形成具有粘塑性的喂料，在加热状态下，利用注射成型机将喂料注入模具模腔内冷凝成型，经过加热去除粘结剂后，便可用于烧结，如图3所示。喂料的流变性是影响注射成型成品质量的一个重要因素，通常我们希望喂料粘度较低，这就要求原料粉末与粘结剂相容性要好，而且混合均匀。

AlN Ceramic Injection Molding (AIM) is a method of powder injection molding (PIM) applied to ceramic powder molding. Based on the plastic injection molding process, the forming technology is produced by technical improvement. The basic process is to add a binder into the AlN powder and mix it evenly to form a viscoplastic feeding material. Under heating condition, the feeding material is injected into the mold cavity for condensation molding by an injection molding machine. After removing the binder by heating, it can be used for sintering, as shown in Figure 3. The rheological property of feeding material is an important factor affecting the quality of injection molding products. Usually we want the viscosity of feeding material to be low, which requires the compatibility of raw material powder and binder to be good, and the mixture is uniform.

优点：

Advantage:

致密度高，密度分布均匀，可用于复杂形态坯体成型，且成型精度高，无需后期机械加工。

High density, uniform density distribution, can be used for complex shape green body molding, and molding precision is high, without the need for post-processing.

缺点：

Shortcomings:

易出现欠注、飞边、熔接痕、气穴等缺陷影响AlN陶瓷烧结。

It is easy to have defects such as under injection, flash, weld mark and cavitation, which affect the sintering of AlN ceramics.

制备好的坯体需要经过高温烧结，才能获得高致密度和优良性能的AlN陶瓷，从而在各个领域得到广泛应用。AlN作为高熔点的强共价键化合物，原子自扩散系数小，烧结出致密零件难度大，必须选择合适的烧结方法，并严格控制烧结条件，才能制得具有高致密度和所需优良性能的AlN陶瓷。

AlN ceramics with high density and excellent properties can be obtained by high temperature sintering of the prepared green body, which is widely used in various fields. AlN, as a strong covalent bond compound with high melting point, has a small atomic self-diffusion coefficient and is difficult to sinter compact parts. It is necessary to select a suitable sintering method and strictly control the sintering conditions in order to produce AlN ceramics with high density and good properties.

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常见的AlN烧结方法

Common AlN sintering methods

烧结是指陶瓷粉体经压力压制后形成的素坯在高温下的致密化过程,在烧结温度下陶瓷粉末颗粒相互键联，晶粒长大，晶界和坯体内空隙逐渐减少，坯体体积收缩，致密度增大，直至形成具有一定强度的多晶烧结体。

Sintering refers to the densification process of green body formed by pressing ceramic powder at high temperature. At the sintering temperature, ceramic powder particles bond with each other, grain growth, grain boundaries and voids in green body gradually reduce, green body volume shrinkage, density increase, until the formation of a certain strength of polycrystalline sintered body.

氮化铝作为共价键化合物，难以进行固相烧结。通常采用液相烧结机制，即向氮化铝原料粉末中加入能够生成液相的烧结助剂，并通过溶解产生液相，促进烧结。

As a covalent bond, aluminum nitride is difficult to solid phase sintering. The liquid phase sintering mechanism is usually adopted, that is, adding sintering additives to the powder of aluminum nitride raw material to form liquid phase, and producing liquid phase through dissolution to promote sintering.

AlN烧结动力：粉末的比表面能、晶格缺陷、固液相之间的毛细力等。要制备高热导率的AlN陶瓷，在烧结工艺中必须解决两个问题：第一是要提高材料的致密度，第二是在高温烧结时，要尽量避免氧原子溶入的晶格中。常

AlN sintering power: specific surface energy, lattice defect, capillary force between solid and liquid phases, etc. In order to prepare AlN ceramics with high thermal conductivity, two problems must be solved in the sintering process: first, to increase the density of the materials; second, to avoid oxygen atoms dissolving into the lattice when sintering at high temperature. often