Pressurelessly sintered zirconium diboride/silicon carbide composite bodies and a method for producing the same

Abstract

A method of sintering a ZrB 2 —SiC composite body at ambient pressures, including blending a first predetermined amount of ZrB 2 powder with a second predetermined amount of SiC powder, wherein both powders are characterized by the presence of surface oxide impurities. Next the blended powders are mixed to yield a substantially homogeneous powder mixture and a portion of the substantially homogeneous powder mixture is formed into a green body. The body is fired to a first temperature, wherein substantially all surface oxide impurities are reduced and/or volatilized to substantially eliminate oxides from the green body, and the body is heated to a second temperature and sintered to yield a composite body of at least about 99 percent theoretical density and characterized by SiC whisker-like inclusions distributed substantially evenly in a ZrB 2 matrix.

1 . A pressurelessly sintered ZrB 2  composite body, comprising from about 1 weight percent to about 25 weight percent SiC with the rest being substantially ZrB 2 , wherein the composite material is substantially free of oxide impurities and wherein SiC is present as a substantially uniformly distributed whisker-like phase in a ZrB 2  matrix. 
     
     
         2 . The pressurelessly sintered ZrB 2  composite body of  claim 1  wherein the body is about 99 percent theoretically dense. 
     
     
         3 . The pressurelessly sintered ZrB 2  composite body of  claim 1  wherein body has a porosity of no more than 1 percent. 
     
     
         4 . The pressurelessly sintered ZrB 2  composite body of  claim 1  wherein the SiC whiskers are generally between about 10 and about 20 μm in length. 
     
     
         5 . A method of sintering a ZrB 2 —SiC composite body at ambient pressures, comprising in combination:
 a) blending a first predetermined amount of ZrB 2  powder with a second predetermined amount of SiC powder, wherein both powders are characterized by the presence of surface oxide impurities;   b) mixing the blended powders to yield a substantially homogeneous powder mixture;   c) forming a portion of the substantially homogeneous powder mixture into a green body;   d) reducing surface oxide impurities to eliminate oxides from the green body; and   e)sintering the green body to yield a sintered body with no more than 2 percent porosity.   
     
     
         6 . The method of  claim 5  further comprising after (c) and before (e), volatilizing B 2 O 3  from the green body. 
     
     
         7 . The method of  claim 5  further comprising after a) and before b), adding a reducing agent to the blended powders. 
     
     
         8 . The method of  claim 7  wherein the reducing agent is selected from the group carbon black, graphite, boron carbide, WC, ZrC, HfC, Mo 2 C, and NbC or combinations thereof. 
     
     
         9 . The method of  claim 7  wherein the reducing agent is carbon and wherein oxygen is removed from the green body as gaseous carbon monoxide and gaseous carbon dioxide. 
     
     
         10 . The method of  claim 5  wherein during d), the green body is under a partial vacuum. 
     
     
         11 . The method of  claim 10  wherein oxygen is removed from the green body as a gaseous oxide. 
     
     
         12 . The method of  claim 5  wherein the d) occurs at about 1650 degrees Celsius in a partial vacuum and e) occurs at about 2050 degrees Celsius in an inert gas atmosphere. 
     
     
         13 . A method of preparing a ZrB 2 —SiC composite material, comprising:
 (a) blending between about 2 weight percent and about 25 weight percent SiC, between about 0.1 and about 4 weight percent carbon source material with ZrB 2  to produce a substantially homogeneously blended powder mixture;   (b) forming a portion of the substantially homogeneously blended powder mixture into a green body;   (c) soaking the green body at a temperature or from about 400 to about 600 degrees Celsius in an inert atmosphere to substantially eliminate any present organic and resin materials;   (d) heating the green body in a substantially oxygen-free environment to a temperature sufficient to cause the C to react with any SiO 2  present to form SiO, CO 2 , CO and SiC and to produce a partially-sintered body;   (e) heating the partially-sintered body in an inert gas atmosphere to a temperature sufficient to sinter the partially-sintered body to produce a substantially theoretically dense sintered body.   
     
     
         14 . The method of  claim 13  wherein the substantially theoretically dense sintered body is characterized by substantially evenly distributed SiC whisker phase uniformly dispersed in a ZrB 2  matrix. 
     
     
         15 . The method of  claim 13  wherein the substantially theoretically dense sintered body is characterized by a SiC whisker phase substantially evenly distributed in a ZrB 2  matrix. 
     
     
         16 . The method of  claim 15  wherein the SiC whiskers are generally about 10 to 20 μm in length. 
     
     
         17 . The method of  claim 13  wherein the substantially theoretically dense sintered body has a porosity of no more than 1 percent. 
     
     
         18 . A method of producing a pressurelessly sintered ZrB 2 —SiC composite body substantially free of oxide impurities with a composition of about 1 weight percent to about 25 weight percent SiC present as a substantially uniform distribution of SiC whiskers, with the rest being a substantially ZrB 2  matrix, comprising the steps of:
 (a) mixing between about 2 weight percent and about 25 weight percent SiC powder, between about 0.1 and about 4 weight percent reducing agent, and about 1 weight percent to about 5 weight percent binder material with ZrB 2  powder to produce a substantially homogeneously blended powder mixture, wherein oxide impurities are present in the SiC and ZrB 2  powders;   (b) forming a portion of the substantially homogeneously blended powder mixture into a green body;   (c) heating the green body to at least about 400 degrees Celsius in an inert atmosphere;   (d) substantially reducing oxide impurities present in the green body;   (e) placing the green body in an inert gas atmosphere and elevating the temperature of the green body to a temperature sufficient for sintering to progress; and   (f) soaking the green body in an inert gas atmosphere at a temperature sufficient for sintering to progress for sufficient time to yield a substantially theoretically dense sintered body.   
     
     
         19 . The method of  claim 18  wherein during f) the temperature sufficient for sintering to progress is about 2100 degrees Celsius and sufficient time to yield a substantially theoretically dense sintered body is about 4 hours. 
     
     
         20 . The method of  claim 18  wherein the substantially theoretically dense sintered body is characterized by SiC whiskers substantially evenly dispersed in a ZrB 2  matrix. 
     
     
         21 . The method of  claim 18  wherein the reducing agent is carbon. 
     
     
         22 . The method of  claim 18  wherein between about 2 and about 4 weight percent B 4 C powder is added during (a). 
     
     
         23 . The method of  claim 18  wherein the reducing agent is selected from the group carbon black, graphite, boron carbide, WC, ZrC, HfC, Mo 2 C, and NbC or combinations thereof 
     
     
         24 . A low-pressure method of producing a substantially dense sintered SiC—ZrB 2  composite body substantially free of oxide impurities with a composition of about 1 weight percent to about 25 weight percent SiC present as a substantially uniform distribution of SiC whiskers, with the rest being a substantially ZrB 2  matrix, comprising the steps of:
 (a) mixing between about 1 weight percent and about 25 weight percent Si-source powder, between about 1 and about 5 weight percent B-source powder, between about 0.1 and about 4 weight percent reducing agent, and about 1 weight percent to about 5 weight percent binder material with Zr-source powder to produce a substantially homogeneously blended powder precursor mixture, wherein oxide impurities are present in the Si- and Zr-source powders;   (b) forming a portion of the substantially homogeneously blended powder precursor mixture into a green body;   (c) substantially volatilizing any binder present in the green body;   (d) substantially carbonizing any resin present in the green body;   (e) substantially reducing oxide impurities present in the green body;   (f) placing the green body in an inert gas atmosphere and elevating the temperature of the green body to a temperature sufficient for sintering to progress; and   (g) soaking the green body in an inert gas atmosphere at a temperature sufficient for sintering to progress for sufficient time to yield a substantially theoretically dense sintered SiC—ZrB 2  body.   
     
     
         25 . The method of  claim 24  wherein the Si-source powder is SiC, wherein the B-source powder is ZrB 2 , and wherein the Zr-source powder is ZrB 2 . 
     
     
         26 . The method of  claim 24  wherein the Si-source powder is metallic Si, wherein the B-source powder is B 4 C, and wherein the Zr-source powder is metallic Zr. 
     
     
         27 . The method of  claim 24  wherein the Si-source powder is SiC, wherein the B-source powder is B 4 C, and wherein the Zr-source powder is ZrB 2 .