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Reaction Densification of -SiAION: II, Densification Behavior
-SiAION的反应 致密化:II,致密化行为

Mohan Menon and I-Wei Chen*
莫汉·梅农(Mohan Menon)和陈怡薇(I-Wei Chen)*
Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136
密歇根大学材料科学与工程系, 密歇根州安娜堡 48109-2136

Reaction hot-pressing behavior of , and powder mixtures , Dy, Er, and Yb) forming -SiAION has been studied. Five characteristic temperatures are found to control the densification behavior of these materials. The densification proceeded in three major stages. The first two stages were formation of ternary oxide eutectic and wetting of majority nitride powder. The third stage involved dissolution/melting of intermediate phase. Variation from this behavior sometimes occurs due to localization of wetting liquid at AIN, extremely high melting/dissolution temperature of and and melilite, and secondary precipitation of Dy- -SiAION. The dominant densification mechanism was found to be massive particle rearrangement, irrespective of the wetting and dissolution/melting behavior. The efficiency of this mechanism is mostly affected by the amount of available liquid and less by its viscosity. Fully dense, single-phase ceramics were obtained in all cases except Mg when hot-pressed at a constant heating rate to , and considerably lower temperatures for , Gd, Dy, Er, and Yb-SiAION when held isothermally.
研究了 粉末混合物 、Dy、Er和Yb)形成 -SiAION的反应热压行为。发现五种特征温度可以控制这些材料的致密化行为。致密化分三个主要阶段进行。前两个阶段是三元氧化物共晶的形成和多数氮化物粉末的润湿。第三阶段涉及中间相的溶解/熔化。这种行为的变化有时是由于润湿液在AIN的局部化, 和melilite的极高熔化/溶解温度 ,以及Dy- -SiAION的二次沉淀。主要的致密化机制是大量的颗粒重排,而与润湿和溶解/熔融行为无关。这种机制的效率主要受可用液体量的影响,而受其粘度的影响较小。在所有情况下,除了以恒定加热速率热压至 Mg时,以及当保持等温时 ,Gd、Dy、Er和Yb-SiAION的温度要低得多,因此在所有情况下都获得了全致密的单相陶瓷。

I. Introduction 一、引言

S INCE the concept of "transient liquid sintering" was introduced, intensive investigations have been done on the reaction sintering of SiAION in the metal oxide- system. Some of the earliest work was carried out in the system by Lewis et al. They found that a transient phase which formed during the hotpressing of with reacted with above to form and a vitreous phase. This reaction was found to expedite the sintering kinetics. Further, they found that the sintering kinetics and the reaction pathway of a mixture of depended on the amount of The addition of , instead of to a mixture resulted in a sample with diphasic SiAION (YAG) microstructure with improved mechanical properties. Boskovic al. used the concept of transient liquid sintering to obtain dense -SiAlON ceramics in the plane. In their study, they too found that the sintering kinetics depended on the composition of starting powder mixtures, even though the final composition was the same. In these and other reaction hot-pressing studies, the densification mechanisms were identified to be either solution-reprecipitation, fast particle rearrangement, Coble creep, or grain boundary sliding. 9,11
引入了“瞬态液体烧结”的概念,对SiAION在金属氧化 体系中的反应烧结进行了深入研究。 一些最早的工作是由Lewis等人在 系统中进行的。 他们发现,在 热压过程中形成的瞬态相与 上面 的玻璃 相反应形成。 发现该反应可以加速烧结动力学。此外,他们发现,混合物的烧结动力学和反应途径 取决于 添加量,而不是 添加到 混合物中,从而使样品具有具有改进的机械性能的双相 SiAION (YAG)微观结构。 Boskovic 等人使用瞬态液体烧结的概念在 平面上获得了致密 的-SiAlON陶瓷。 在他们的研究中,他们也发现烧结动力学取决于起始粉末混合物的成分,即使最终成分相同。在这些和其他反应热压研究中,致密化机制被确定为溶液再沉淀、 快速颗粒重排、 Coble 蠕变 或晶界滑动。9,11
Recently, Hwang and Chen found that reaction hot pressing of and -SiAlON took place in three stages. Further, they found that the wetting properties of the eutectic melt controlled the densification behavior of the powder compact. The first stage was identified with the
最近,Hwang和Chen发现 -SiAlON的反应热压分三个阶段进行。 此外,他们发现 共晶熔体的润湿性能 控制了粉末压块的致密化行为。第一阶段被确定为
formation of the ternary oxide eutectic and YAG. The shrinkage in this stage was due to the redistribution of liquid in the powder compact and slight improvement in the packing efficiency. The second stage was identified with the wetting of AIN particles and formation of . The preferential wetting of AlN by the ternary oxide melt caused localization of the liquid, leading to a delaying effect on the second shrinkage step. The third stage occurred with the dissolution of and formation of the final phase. Massive particle rearrangement was found to be the dominant densification mechanism. It also caused enrichment in the liquid, leading to formation of as a transient phase. Thus the physical/chemical characteristics of the liquid, in particular its wetting behavior, and the kinetic pathway of the intermediate reactions are clearly important factors in reaction densification of multicomponent systems.
三元氧化物共晶和YAG的形成。这一阶段的收缩是由于液体在粉末压实中的重新分布和包装效率的略有提高。第二阶段是AIN颗粒的润湿和形成 。三元氧化物熔体对AlN的优先润湿导致液体局部化,导致第二收缩步骤的延迟效应。第三阶段随着最后阶段的 解散和形成而发生。发现大量颗粒重排是主要的致密化机制。它还导致 液体富集,导致 形成瞬态相。因此,液体的物理/化学特性,特别是其润湿行为,以及中间反应的动力学途径显然是多组分体系反应致密化的重要因素。
The preceding paper (part I) has provided a broad picture of the wetting behavior of the ternary oxides and reaction pathways in the system , Dy, Er, and Yb). Generally, the more basic oxides wet , whereas the more acidic oxides wet AIN. It has also identified temperatures for the various reactions which can be used to
前面的论文(第一部分) 提供了三元氧化物的润湿行为和反应途径在 体系 中,Dy、Er和Yb的润湿行为。 一般来说,碱性氧化物越多 ,而酸性氧化物就越湿。它还确定了可用于
(a)
(b)
Fig. 1. Schematic shrinkage curves when the eutectic melt wets (a) , and (b) AIN first.
图 1.共晶熔体先润湿(a) 和(b)AIN时的收缩曲线示意图。

Manuscript No. 193383. Received August 3, 1994; approved October 17, 1994 Supported by the National Science Foundation under Grant No. DDM-9024975. "Member, American Ceramic Society.
手稿编号 193383.收稿日期: 1994-08-03;1994 年 10 月 17 日批准 由美国国家科学基金会资助,资助号为DDM-9024975 中。“美国陶瓷学会会员。

understand the shrinkage behavior. The reactions identified during the reaction densification of -SiAlON are (i) the eutectic formation (at temperature ), (ii) wetting of a nitride powder and intermediate phase precipitation (at temperature ), (iii) secondary wetting of the other nitride powder (at temperature ), (iv) dissolution of the intermediate phase (at temperature ), and (v) precipitation of the final phase, -SiAION (at temperature ). Figures and (b) show the schematic of expected shrinkage curves when the eutectic melt preferentially wets and , respectively. In these curves, the beginning of various shrinkage steps are identified with some of the above characteristic temperatures. Wetting of AIN is shown to lead to small or no immediate shrinkage in the powder compact because of the low AIN content of the typical SiAION compact. In Fig. 1(b), though, a subsequent shrinkage step occurs when the majority is wetted. Variation of these shrinkage curves may also be possible. For example, it is known that the initial precipitation of the intermediate phase usually starts with partial wetting of the first nitride; i.e., could be significantly lower than the temperature when complete wetting is achieved. Also, the dissolution of intermediate phase may or may not precede the precipitation of -SiAlON; i.e., may or may not be higher than . Indeed may even be lower than , as shown later.
了解收缩行为。 在-SiAlON反应致密化过程中确定的反应是(i)共晶形成(在温度 下),(ii)氮化物粉末的润湿和中间相沉淀(在温度 下),(iii)其他氮化物粉末的二次润湿(在温度 下),(iv)中间相的溶解(在温度 下),以及(v)末相 -SiAION的沉淀(在温度 下)。 和(b)分别显示了共晶熔体优先润湿 时的预期收缩曲线示意图。在这些曲线中,各种收缩步骤的开始被识别为上述一些特征温度。由于典型SiAION压块的AIN含量低,AIN的润湿会导致粉末压块的微小收缩或没有立即收缩。 然而,在图1(b)中,当大部分 被润湿时,会发生随后的收缩步骤。这些收缩曲线的变化也是可能的。例如,众所周知,中间相的初始沉淀通常从第一氮化物的部分润湿开始;即, 当实现完全润湿时,温度可能明显低于温度。 此外,中间相的溶解可能先于 -SiAlON沉淀,也可能不先于-SiAlON沉淀; 即, 可能高于 ,也可能不高于 。事实上 甚至可能低于 ,如后所示。
In this paper, we report the densification behavior during the reaction hot pressing of -SiAlON system with metal oxide additions . Hot pressing was applied to provide a constant driving force for densification. The characteristic temperatures discussed above are identified for various systems using shrinkage data and information from part I. The role of wetting behavior of the ternary oxide melt and the formation/dissolution of intermediate phases in densification is then assessed along with other kinetic considerations such as amount and viscosity of the liquid. Some general conclusions are drawn from these comparisons to further our understanding of reaction densification of these complex systems.
本文报道了 -SiAlON体系与金属氧化物添加反应热压过程中的致密化行为 。采用热压为致密化提供恒定的驱动力。上面讨论的特征温度是使用收缩数据和第一部分的信息为各种系统确定的。然后评估三元氧化物熔体的润湿行为和中间相的形成/溶解在致密化中的作用以及其他动力学考虑因素,例如液体的量和粘度。从这些比较中得出了一些一般结论,以进一步理解这些复杂系统的反应致密化。

II. Experimental Procedure
二、实验程序

(1) Composition (1)组成

The compositions investigated lie on the so-called -plane represented by the formula . Specifically, , and and (1210) were chosen because they lie inside the single-phase region. The compositions studied are listed in Table I and are the same as reported in part I.
所研究的成分位于由公式 表示的所谓 -平面上。具体来说, 选择 和 (1210) 是因为它们位于单相 区域内。所研究的成分列于表一中,与第一部分报告的成分相同。

(2) Powder Preparation and Hot Pressing
(2)粉末制备和热压

Details of powder preparation and hot pressing are given in part I. Hot-pressing data reported here were obtained from runs at a constant heating rate of to in most cases. The temperature when full density is obtained during the above runs is denoted as . Isothermal runs held at some intermediate temperatures were also performed to approximately locate the lowest temperature, denoted by , required to obtain full density. In addition, densification kinetics were evaluated during isothermal hold for some systems.
粉末制备和热压的细节在第一部分中给出, 这里报告的热压数据是在大多数情况下从恒定加热速率 到的 运行中获得的。在上述运行过程中获得全密度时的温度表示为 。还进行了在一些中间温度下保持的等温运行,以大致定位获得全密度所需的最低温度,用 表示。此外,还评估了某些系统在等温保持期间的致密化动力学。
Table I. Compositions Studied (wt%)
表I. 研究的成分(wt%)
Material Additive AlN
Li 1010 2.63 2.99 12.03 82.35
4.83 2.92 11.76
Mg 1010 3.52 2.96 11.92 81.60
Y 1010 6.37 2.88 11.57 79.18
Nd 1210 10.88 2.20 12.82 74.10
Sm 1210 11.24 2.19 12.76 73.81
Gd 1210 11.63 2.18 12.70 73.49
Dy 1210 11.93 2.17 12.66 73.24
12.20 2.16 12.62 73.02
Yb 1210 12.52 2.15 12.58 72.75

III. Results 三、结果

A summary of the densification behavior is given in Tables II and III. Table II gives the characteristic temperatures, , along with the volume shrinkage for the first two steps. Table III gives the two densification temperatures to reach full density, and , as well as the phase assemblages at . The phase assemblages at are already given in Table II of part for most of the systems.
致密化行为的摘要见表二和表三。表II给出了特性温度, 以及前两个步骤的体积收缩率。表III给出了达到全密度的两个致密化温度, 以及 相组合。对于大多数系统,部分 的相位组合 已经在表II中给出。

(1) Alkali and Alkaline-Earth Oxides
(1)碱土氧化物

The systems studied here were M-1010, M being Li, Ca, and .
这里研究的系统是M-1010,M是Li,Ca和 .
(A) Li System: The shrinkage of the Li-1010 sample contains three well-defined stages (Fig. 2(a)). The first shrinkage step occurs at accompanied by shrinkage. The second step occurs at , accompanied by shrinkage. The third step occurs at . A fourth step occurs at . Full density is achieved at under constant heating rate and can also be achieved at when held over .
(A) Li System:Li-1010 样品的收缩包含三个明确定义的阶段(图 2(a))。第一个收缩步骤发生在 伴随着 收缩。第二步发生在 ,并伴有 收缩。第三步发生在 。第四步发生在 。在恒定的加热速率 下可实现全密度,也可以在 保持时 实现。
For this system, in which wetting of is preferred and is complete at the characteristic temperatures are and , corresponding to the formation of oxide melt, and the wetting of , respectively. The third shrinkage step starting at seems to correspond to the dissolution of the intermediate phase , hence at . Since formation was detected above , according to part yet AlN still remained at after isothermal hold but not at the step at is possibly related to wetting and dissolution of .
对于该系统,其中润湿 是优选的,并且在 特征温度下 完全是 和 ,分别对应于氧化物熔体的形成和 的润湿。从 开始 的第三个收缩步骤似乎对应于中间相 的溶解,因此在 。由于 上面 检测到了地层,因此部分 AlN 在等温保持后仍保持在等温保持处,但在步骤中 未保持,这可能与润 湿和溶解有关。
(B) Ca System: Compared to Li-1010, the shrinkage curve of Ca-1010 has fewer well-separated steps (Fig. 2(b)). However, on closer examination, three shrinkage steps can be identified. The first shrinkage step occurs at . A second step is identified around , followed by continuous gradual shrinkage. A third step at and another at seem to be present. Full density can be achieved at under constant heating rate and also at when held for . Full densification was not possible at .
(B)钙体系:与Li-1010相比,Ca-1010的收缩曲线具有较少的分离步骤(图2(b))。然而,经过仔细检查,可以确定三个收缩步骤。第一个收缩步骤发生在