Protective coating for ceramic matrix composites

1. An article comprising:

a substrate; and

a layer atop the substrate comprising:

a matrix comprising at least one of hafnium silicate (HfSiO 4 ) and ytterbium disilicate (Yb 2 Si 2 O 7 ); and

barium magnesium alumino silicate (BMAS), the layer having a thickness of 0.05 mm to 0.50 mm and a BMAS concentration of 0.8% to 10.0% by weight.

2. The article of claim 1 wherein:

the substrate comprises a ceramic matrix composite.

3. The article of claim 2 wherein:

the ceramic matrix composite is a SiC/SiC ceramic matrix composite.

4. The article of claim 1 wherein:

the article is a blade outer airseal and the layer is along an inner diameter (ID) surface of the blade outer airseal.

5. The article of claim 1 wherein:

the layer is directly atop the substrate.

6. The article of claim 1 wherein:

the layer is an outermost layer.

7. The article of claim 1 wherein:

the layer is an intermediate layer between the substrate and a ceramic layer.

8. The article of claim 1 wherein:

the layer adheres an object in a hole in the substrate.

9. The article of claim 1 wherein:

the layer covers an area of at least 4.0 cm 2 .

10. The article of claim 1 wherein:

the layer adheres an object to the substrate.

11. The article of claim 10 wherein:

the object is a thermocouple.

12. The article of claim 1 wherein:

the layer comprises said hafnium silicate (HfSiO 4 ).

13. A gas turbine engine including the article of claim 1 .

14. The gas turbine engine of claim 13 wherein:

the article is a blade outer air seal.

15. A method for using the article of claim 1 , the method comprising:

exposing the article to a calcium magnesium aluminosilicate (CMAS)-forming environment.

16. A method for manufacturing the article of claim 1 by applying the layer to the substrate, the method comprising:

applying a combination of:

at least one of hafnium oxide (HfO 2 ) and ytterbium oxide (Yb 2 O 3 );

silicon carbide (SiC); and

barium magnesium aluminosilicate (BMAS); and

heating to react the at least one of hafnium oxide (HfO 2 ) and ytterbium oxide (Yb 2 O 3 ) with the silicon carbide (SiC) to form the least one of hafnium silicate (HfSiO 4 ) and ytterbium disilicate (Yb 2 Si 2 O 7 ).

17. The method of claim 16 wherein:

the applying is of one or more slurries.

18. The method of claim 17 wherein:

a weight content of the BMAS relative to total combined HfO 2 , Yb 2 O 3 , SiC, and BMAS in the one or more slurries is 0.8% to 10.0%.

19. The method of claim 17 wherein:

the applying is via ultrasonic spray.

20. The method of claim 16 wherein:

the heating is in an oxidizing environment; and

the heating is to a peak temperature of at least 1450° C.